Explanation #1: Rashi explains that a "quarter" refers to a quarter of a Shekel which equals half of a Dinar.

Proof: It is also implied in Yoma (55b) that these two denominations normally are of equal value. The Gemara asks, why don't we take four Zuz (the value of a bird Chatas) and throw them in the river? Four regular Zuz are half of a Dinar Tzuri, as a Dinar Medinah is one eighth of a Dinar Tzuri. (See the Sefer Yom Teruah on this Tosfos at length to explain how we see from the Gemara in Yoma that a Rova Shekel is a half Dinar.)

Explanation #2: However, in Kerisus (10b) it is clear that a "quarter" refers to a quarter of a Dinar.

Proof: Regarding birds costing a Rova, and the Gemara's statement that the Torah had pity on poor people that they should only offer sacrifices that are worth one sixteenth of a rich person's sacrifice, the Gemara explains that a sheep costs a Sela which equals four Dinar. One sixteenth of that is a quarter of a Dinar. (It must be that the bird offering is one quarter of a Dinar, as this is one sixteenth of the value of a sheep.)

Implied Question: The Gemara in Yoma (ibid.) says four Zuz. (Doesn't this imply that Rashi is correct?)

Answer: This was an extreme case, as sometimes birds are very expensive. [See also Tosfos in Menachos 107b, DH "Keves."]

Observation: In Shevuos (16a), we are unsure whether Rebbi Eliezer holds the original holiness was holy then and in the future forever or not.

Implied Question: We cannot extrapolate anything regarding this question from our Gemara that says that he had to bring it to Yerushalayim. (Why not extrapolate from here that it is holy forever, as he had to bring it to Yerushalayim even in his days?)

Answer: This is because it is a decree that sages already gathered in numbers to decree, as stated in Beitzah (5b, and therefore would require another gathering to nullify this law whether there is still holiness there or not).

Question: If it was not holy, how would the poor benefit? They could not eat it in Yerushalayim if the holiness was no longer present! (It therefore is still a proof that the holiness remained forever according to Rebbi Eliezer!)

Answer: They could put the value of produce worth a Manah (a lot of money) on a Perutah (small copper) coin, as stated in Bava Metzia (57a) that one may take a Manah worth of Hekdesh and put its holiness onto a Perutah coin, and it is a valid transfer (and they could proceed to eat the produce outside of Yerushalayim).

Implied Question: This is despite the fact that in Bava Metzia (ibid.) there is an argument whether doing so is Lechatchilah or b'Dieved. (Why would Rebbi Eliezer instruct them to do something that is forbidden Lechatchilah?)

Answer: The Gemara concludes in Erchin (29a) that nowadays it is considered Lechatchilah to do this.

Implied Question: However, there is no proof from Hekdesh to Ma'aser Sheini and Kerem Revai. This is evident from the Gemara in Gitin (65a) that says that one can use trickery with Ma'aser Sheini. The Gemara says that we are dealing with Ma'aser Sheini nowadays which is only a Rabbinic law. The Gemara asks, is there such a thing as a Jewish maidservant nowadays? The Gemara seemingly should have asked from Ma'aser Sheini itself that no trickery is necessary nowadays, since one can transfer the entire holiness, even the principle and the extra fifth, on a Perutah!

Answer: The Bahag and the Sheiltos of Rav Achai indeed rule that one may transfer the holiness of Ma'aser Sheini or Kerem Revai worth a Manah onto a Perutah. The Gemara in Gitin (65a) indeed could have asked this question (and merely chose not to).