$55 Facing an overbet on the river

I'd fold to the preflop raise.

On the flop, I think raising or folding is much better than just calling. The problem with just calling is that you don't force him to make a mistake if he has overcards (he's only putting in 20 chips into a 200 chip pot to see a turn) and you also have no idea where you stand. I'd raise to 175 or so on the flop and be happy to take it down right there, if he calls and I don't improve, I'm checking the turn and considering calling a small river bet if the board doesn't look too scary.

Given the way you played it, I'm folding the river. In my experience at the lower buy-ins a huge river overbet is more often than not a monster, and I just don't need to go broke here. I'd guess he has a boat, or played AA very strangely.