The best solution would be some PA equipment, but that's not going to be cheap. I'd look for some used Hi-Fi gear at pawn shops, thrift stores, craigslist, yard sales, etc. It shouldn't be hard to find an old receiver and a pair of floor standing speakers for under $100. You might try contacting some of the local pro audio shops (guitar center, etc) and see if they'd let you put a want ad in the store, there's a good chance someone would donate some old gear.
For that matter I've got an older yamaha stereo receiver with a temperamental selector knob (it works but requires a very gentle touch, it could be jumpered internally if you only plan on using one source.) I'd give it to you for free, shipping to would probably cost $25-30, which is more than the receiver is worth though.