Used tranny from u-pull yard near me is $125 plus a core deposit. Some yards have 30 day or longer warranty, some will sell a warranty, etc. And if you don't want to pull it there are usually a group of partz vulturez that will take anything out for like $50 - $100. And there are dismantlers, like Paul Grant on this site, who know a good bit more about the condition of the donor vehicle.

But how much water is required to ruin the tranny vs make fluid discolor? Seems like it must not be that common? We do have a lot of fellows that can't resist mud and water....