I'll second the recommendation for the B&K amps. I you shop around for a ST-140 or ST-202, you'd be able to come in under your budget, and with a nice sounding amp.
best used amp for 300- 400
I have a system composed of a rotel rcd970 cd player, rc990 preamp, rt940 tuner, acoustic reasearch turntable with denon mc cartridge and old infinity Qe speakers and am looking to replace my amp an old dying adcom gfa-2. I have heard a rotel rb 980 in the system and it was decent but not great i am trying to find an old bryston 3b but any suggestions would be welcome, my price range is less than $400 including shipping so closer to $350 would be ideal. I listen mostly to classic rock and ska, so i want power and good bass but also want good upper frequency perfomance as well. Thanks