Join your local facebook aquarium groups and check out craigslist list. I often see people giving away or selling cheap. You can put an ad out letting people know you have the space and you'll likely get a few offers. I've also made some cool connections just talking to people at my LFSs.
Cheap and colorful, can't beat Mbuna. Can get them at any fish store as babies for like 2-3$ a pop usually. They get a lot of flak on MFK because people prefer americans (as do I tbh) but the mbuna are still great fish to keep.