Gemara

52b (Chizkiyah): One can redeem Ma'aser Sheni worth less than a Perutah on coins of Ma'aser, for surely he did not redeem their full value.

Question (Mishnah): Terumah and Bikurim can become Batel in 100 parts of Chulin, but Ma'aser cannot.

Inference: Ma'aser is Batel in a majority of Chulin!

If one can redeem even less than a Perutah of Ma'aser, it is Yesh Lo Matirim (it can be permitted in some way). If so, it is never Batel!

Answer: The case is, he has no prior coins.

Yevamos 81b (Beraisa): If a Tahor piece of a Chatas or Lechem ha'Panim was mixed with 100 Tahor Chulin pieces, all agree that it is not Batel.

82a (Rav Ashi): It is Davar she'Yesh Lo Matirim, so it is never Batel.

Rejection: This is wrong! For a Kohen, the piece is always permitted! For a Yisrael, it is always forbidden!

Avodah Zarah 73b (Beraisa): If Tevel was mixed b'Mino, it forbids b'Mashehu. If it was mixed Lo b'Mino, it forbids b'Nosen Ta'am.

We are more stringent about Tevel than about other Isurim, for its Isur resembles the Heter (the way it becomes permitted):

(Shmuel): Separating even a tiny amount of Terumah permits any quantity of Tevel (mid'Oraisa).

Rishonim

Rashba (Toras ha'Bayis ha'Katzar 4:4 38a, brought in Beis Yosef YD 102 DH v'Chosav): If a Kli that absorbed Isur became mixed with others and the forbidden Kli is not recognizable, it is Batel in a majority. Even though one could Kasher it, we do not consider it like Davar she'Yesh Lo Matirim and forbid until he Kashers all the Kelim. Rather, it is like a dry Isur that became mixed with dry Heter. It is Batel in a majority. Whenever the Isur is not permitted automatically, and one must spend money, it is not considered Davar she'Yesh Lo Matirim. (Beis Yosef - the Tur wrote so in Siman 122.)

Tosfos (Avodah Zarah 73b DH Tevel): The Yerushalmi says that any amount of Tevel forbids because it is Yesh Lo Matirim. Both reasons are needed. Yesh Lo Matirim applies only when the owner is in the city, and could take Terumah and permit it. If one would need to toil and spend money to go to where the owner is, it is like Ein Lo Matirim. R. Tam explained like this in Bava Metzia. 'The Isur resembles the Heter' applies only to Terumah, but not to Ma'aser Rishon from which one must take a tenth to be Terumas Ma'aser.

Beis Yosef (YD 122:8 DH Kosav ha'Rashba): The Rashba says that when one has other produce to tithe from, he can permit without loss so it is Yesh Lo Matirim. In Avodah Zarah we discuss when he has no other produce. Bava Metzia proves this. Chizkiyah holds that Ma'aser is Ein Lo Matirim when he has no prior coins. We do not say that he can buy Tevel, tithe it and redeem the Ma'aser, so he will have prior coins! A Mishnah in Chalah (3:9) says that even if he has no other produce, Teve is Davar she'Yesh Lo Matirim! The Ramban (Avodah Zarah 73b DH Zeh) says that when one must tithe everything and lose much Heter, this is Ein Lo Matirim. The same applies when one would need to Kasher all the Kelim.

Tosfos ha'Rosh (53a DH Chetzi, citing R. Shlomo of Travyash): The Gemara could not explain that Tevel is not Batel due to Yesh Lo Matirim, for Chachamim would decree not to tithe on Tevel mixed with Chulin, lest one buy Vadai Tevel. (This is like the decree not to redeem less than a Perutah of Ma'aser together with other Ma'aser.) The decree would make Tevel Ein Lo Matirim, and it could be Batel! We do not need R. Tam's poor answers to this question.

Tosfos (Bava Metzia 53a DH Lihader): The Gemara suggested that Ma'aser should be Batel, i.e. when it is far from Yerushalayim and it is Ein Lo Matirim (for it is a toil and costly to take it to Yerushalayim to permit it).

Terumas ha'Deshen (170): If meat was not salted for three days, and it became mixed with other pieces, it is Batel (in a majority). One may cook the entire mixture (in water). Even though even unsalted meat is permitted through roasting, it is not Davar she'Yesh Lo Matirim, for it was never forbidden to roast the unsalted meat, and it will never be permitted to cook it. Yesh Lo Matirim is only when the very matter forbidden can become permitted. The Mordechai (Chulin 665) says that if bread was baked with roasting meat, the Rif calls this Davar she'Yesh Lo Matirim because it can be eaten with meat, and Avi ha'Ezri considers it Ein Lo Matirim, for it was never forbidden with meat, and will never be permitted with milk. Maharam says that we normally rule like the Rif when Tosfos does not argue. However, Avi ha'Ezri's opinion is primary. We conclude that Chatas is Ein Lo Matirim, for it was always permitted to Kohanim, and will never be permitted to Yisre'elim. This is like Avi ha'Ezri. One could distinguish, but Davar she'Yesh Lo Matirim is mid'Rabanan, so we are not so meticulous to be stringent. Even if the piece was Chatichah ha'Reuyah Lehiskaved (a piece fitting to honor guests with), it is Batel, for it is not forbidden due to itself, rather, due to the blood absorbed. Even though we measure (to forbid a mixture) based on the entire piece, for we do not know how much blood is inside, the importance of the piece is not due to the blood, rather, to the piece itself, which is permitted. We distinguish like this regarding other Isurim.

Yam Shel Shlomo (Chulin 8:86): The Terumas ha'Deshen says that meat that was not salted for three days is Ein Lo Matirim. Even though all could be roasted, the Isur, i.e. cooking it, is never permitted. It is unlike an egg (laid on Yom Tov). There the very matter forbidden today (eating it) will be permitted tomorrow. The Terumas ha'Deshen holds that any Isur that is not Batel even in 1000, such as Chatichah ha'Reuyah Lehiskaved, something normally sold by number, or a whole creation, is only when it itself is forbidden. However, Davar she'Yesh Lo Matirim is different. It is never Batel. This primarily affects Chametz during Pesach. All the more so, if unsalted meat became mixed with salted pieces, and one does not have enough salt to salt all the pieces or does not want to do so lest it blunt the meat's taste, all are permitted. Davar she'Yesh Lo Matirim is only if it becomes permitted later, automatically. The Rashba says that it does not apply if one must spend money to permit it. He did not need to mention money. Any Heter that does not come automatically is Ein Lo Matirim.

Rebuttal (Shach YD 102:8): Nedarim is called Yesh Lo Matirim, even though the Heter does not come automatically through time! The Ro'oh (in Bedek ha'Bayis) argues with the Rashba. He says that Yesh Lo Matirim is not why absorptions are not Batel. Rather, any recognizable Isur is not Batel. Since one can remove the Isur through Kashering, it is as if the Isur is recognizable. Further, the Kli will give forbidden taste to Heter. The Maharil argues with the Rashba, because the cost of Kashering is small. We say that Ma'aser Sheni is Yesh Lo Matirim because one can take it to Yerushalayim (even though there is a small expense). One should be concerned for his words when no big loss will result. I say that one should wait until the Kelim are not Bnei Yoman (24 hours after they absorbed Isur), for then they are permitted mid'Oraisa. Mas'as Binyamin (Chidushei Dinim YD 4) says so about using all of them together, but not to use one of them; since it is a mere (absorbed) taste, it is not Davar she'Yesh Lo Matirim. I say that one must wait 24 hours even before using one of them, since the Rashba and Tur permit only because the Heter costs money, and after 24 hours the Torah permits them for free! I wrote (Sa'if Katan 9) that also taste is not Batel (when Yesh Lo Matirim).

Poskim

Shulchan Aruch (YD 102:3): If a Kli that absorbed Isur became mixed with others and the forbidden Kli is not recognizable, it is Batel in a majority. We do not consider it like Davar she'Yesh Lo Matirim.

Rema: This is because one would need to spend money to Kasher it. The same applies to all similar cases.

Question (Taz 8): Why did the Rashba and Rema need to say that it is Ein Lo Matirim because the Heter costs money? In any case, something Ne'esar (it became forbidden due to something else) cannot forbid more than the Oser (what forbade it)! The Isur itself is Ein Lo Matirim, so it can be Batel! Tosfos (Chulin 108b DH Amai) and the Tur (105) say so about salt that absorbed blood.

Answer (Taz): Since the Keli is Yesh Lo Matirim, we do not rely on any reasoning to be lenient, since we can permit without it. We can learn from here to unsalted meat (YD 69:14); the Rema says 'the same applies to all similar cases' to allude to this. Even though one may use all the Kelim, he should not leave them like this a long time without Kashering them, for it is like a dry Isur mixed with Heter: one may not consume all of them together. Here we must be concerned lest he eventually forget the Isur and eat something cooked in all of the mixed Kelim, which is forbidden.

Bach (102 Sof DH u'Mah she'Chosav Aval): It would seem that we are lenient about a mere absorption without any real substance. However, the Rashba disagrees. He applies Yesh Lo Matirim to a Keli that absorbed Isur, because the Heter does not come by itself. The Ran and Terumas ha'Deshen agree. Also the Rambam (Nedarim 5:12) forbids a barrel due to one drop of wine, even though it is not intact. One may not rely on Isur v'Heter, who permits.