for $50 you can pick up a pair of cheap $25-30 speakers paired with a small budget amp like the lepai 2020 or similar. you can get monoprice new or perhaps a pair of used budget speakers from a slightly better level. other solutions include pc speakers like the z313 or creative a250.
if you can stretch your budget up to around $70 you could get something like the micca mb42, dayton b652 or similar paired with a cheap amplifier like a lepai 2020. pc speaker options like the z333
for $80 solutions like the m-audio av32 can be had. pc speakers like the z523 are available.
for $100 you can get into things like the mackie cr3.
bookshelf speakers targeted towards hifi will sound better than pc speakers but without a subwoofer will lack a...