I'm not in a bathroom long enough to appreciate any sound in there, will be the last room I'll add audio into in any case, rather have the kitchen setup instead, which is probably my next "room" after some work I need to do in there on counters/floor.
As to a cheap amp if space isn't a big deal, I'd probably cruise craigslist for a used receiver of some sort. Maybe
something like this (or review the other testing they've done on similar inexpensive amps) for something small.