Gemara

60b (Rav Huna): Plishtim were hiding in stacks of barley of Yisrael. David asked whether he may use others' money (burn the stacks) to save himself. The Sanhedrin answered that a commoner may not, but a king may.

81b (Beraisa): If Levi was lost in a vineyard, David may cut vines until he helps him find his way. Similarly, Levi himself may cut vines until he finds his way.

One might have thought that one may cut vines only if he knows the way. If not, he must backtrack without cutting vines. The Seifa teaches that this is not so.

Question: Why is this listed among enactments of Yehoshua? It is mid'Oraisa!

(Beraisa): "You will return him" teaches that it is a Mitzvah to return another's body (help him find his way if he is lost).

Answer: Mid'Oraisa, one may not harm another's property to help him. Yehoshua enacted that he may cut vines for this.

117b: Reuven was holding a wallet with communal funds for Pidyon Shevuyim (redeeming captives). Robbers came; he gave it to them. Rabah exempted him.

Objection (Abaye): He saved himself with another's money!

Answer (Rabah): The money was for Pidyon Shevuyim. He redeemed himself!

Reuven had brought his donkey on a ferry. The ferry was in danger of sinking; Shimon threw the donkey overboard, and it drowned. Rabah exempted him.

Objection (Abaye): He saved himself with another's money!

Answer (Rabah): Reuven threatened their lives by bringing the donkey aboard!

Sanhedrin 74a (Rava): If Levi was Rodef Ploni and Ploni broke someone else's Kelim, he is liable. One may not save himself with another's money.

Kidushin 8b - Question (Rav Mari): If a dog was chasing Leah, and David was Mekadesh her with a loaf, and she said 'give it to the dog', is she Makneh herself with the Hana'ah of being saved? Or, can she say 'you were obliged to save me!'

This question is unresolved.

(Beraisa): If one said 'be Mekudeshes to me with a loaf', and she said 'give it to this Oni', she is not Mekudeshes, even if the Oni relied on her for his food.

This is because she can say 'also you must feed Aniyim.'

Rishonim

The Rif (44a) brings the Gemara on 117b.

Rambam (Hilchos She'elah 5:1): If money for Pidyon Shevuyim was deposited with Reuven, and robbers came and he gave it to them to save himself, he is exempt. This is the ultimate Pidyon Shevuyim. If the money was designated for particular captives, he must pay.

Ra'avad (in Shitah Mekubetzes 117b DH uv'Emes): If Levi was Rodef Ploni, and Ploni broke Kelim of anyone other than Levi, he is liable, for he may not save himself with others' property. Even if he is Anus, the Ones is not due to the owner of the Kelim. Similarly, one lost in a vineyard erred himself; the owner is not at fault. Even though he pays, Yehoshua needed to stipulate to permit cutting branches not in front of the owner. However, why was David unsure? Even if you will say that he had not heard about Yehoshua's stipulation, why did the Sanhedrin permit only for a king? Rather, they said that only a king may do so without paying. If so, one may save himself with Ploni's money whether or not Ploni is there, provided that he will pay him.

Rosh (Bava Kama 6:12): David did not ask whether he may burn others' property to save Yisre'elim. One may transgress anything for Piku'ach Nefesh other than the three Aveiros! Rather, he asked whether he may burn them without intent to pay for them. The answer was that one may not save without intent to pay.

Rashi (60b DH v'Yatzilah): The Sanhedrin ruled that he may not burn the stacks, for one may not save himself with another's money.

Mordechai (193): The one who threw the donkey overboard was exempt because it was dangerous to bring it aboard. If it were normal to bring a donkey on a ship (e.g. nowadays) and it started acting wildly and threatened to sink the ship, one who threw it overboard would be liable, in spite of the mortal danger. The entire Sugya obligates one who used another's money to save himself from mortal danger. One who was Moser due to mortal Ones is exempt. If witnesses signed Sheker due to mortal Ones, they are Kesherim and exempt from paying. If it was ccsssvsssscacamonacccccccetary Ones, they are Pasul for testimony and liable for the loss they caused. Perhaps even regarding mortal Ones, one must pay if he did an overt action.

Poskim

Shulchan Aruch (CM 359:4): Even if one is in mortal danger and must steal to save himself, he may take only with intent to pay.

Chasam Sofer (OC 208 DH u'Mah she'Chosav): Witnesses may sign Sheker to save themselves, but they should pay from their money to the one will lose due to this.

Afikei Yam (2:32 DH uv'Emes): Others are commanded to use their money to save Ploni. Why can't Ploni use others' money to save himself? Rashi forbids this when the others are not there, for then they are not obligated. It seems that Tosfos and the Rosh obligate one who saved himself with another's money only because one who saves need not do so from his own money.

Hafla'ah (Kesuvos 19a Tosfos DH v'Omar): Rav Chisda discussed only an Anas who intended to kill the witnesses. (In CM 292 and 388, we distinguish whether or not the Anas intended to take from the one he confronted.) Then, they may not exempt themselves by signing Sheker against another. He forbids to steal from or cause a loss to another to heal oneself. Rava replied that even in this case, we permit anything except for the three Aveiros.

Binyan Tziyon (168): The Hafla'ah holds that Tana'im and Amora'im argue about whether or not Levi may save himself with another's money if the Anas came to kill Levi.

Gilyon Maharsha: If one merely needs to use another's item for Piku'ach Nefesh, he should take it with intent to pay rental.

Shulchan Aruch (CM 380:3): If Levi was Rodef Ploni and Ploni broke someone else's Kelim, he is liable. One who saves himself with another's money is liable.

Shach (378:2): The Shulchan Aruch obligates one who damaged b'Ones. The Rema exempts if it was total Ones. I say that if he intended, he is liable even for total Ones, like a Nirdaf who broke Kelim.

Rebuttal (Or Gadol p.20): We learn that Ones is exempt from "you will not punish the Na'arah Me'orasah (who was raped)". Ones exempts from Misah even if one intended to sin; the same applies to damages. The Minchas Chinuch says that we exempt one who transgressed due to Ones for that Aveirah, but not for Ones of illness. Likewise, we exempt only if the Anas wanted Ploni's money, but not if he Stam demanded money.

Yam Shel Shlomo (10:47): A Moser is only Gerama, so he is exempt if he was coerced. If he picked up the item, he acquired it to be liable for it.

Gilyon Maharsha: Here he is liable even though he did not pick it up! Rather, here he is liable because he was not forced to break. There, he was forced to hand over the item (therefore he is liable only because he acquired it).