Bechorot 11 - How Much for a Firstborn Donkey?
The preferred method of redeeming a firstborn donkey is to give the kohen a sheep. A generous person gives a sheep worth 4 zuz, stingy - 2 zuz, and average - 3 zuz, and a zuz is $50. However, even a very lean sheep worth $10 will also make the redemption. Alternatively, one can give anything of value, even cooked vegetables, but then the amount should be equal to the worth of the donkey.
If one redeems his fellow's firstborn donkey, it is valid. Does he acquire the donkey? Do we say that it is similar to consecrated property, and the redeemer acquires it, or do we say that it still belongs to the owner, since he could have redeemed it with a very cheap sheep? The answer comes from the rule about stealing a firstborn donkey. If a thief were to steal it, he would pay the owner double, the usual penalty for stealing from an individual, and not single, the penalty for stealing consecrated property. We see then that it belongs to the owner, and we can conclude that it is not like consecrated property, and that the redeemer does not acquire it.
Art: Vincent Van Gogh - Still Life With Vegetables And Fruit