For your price $500 try to find a clean Yamaha P2200 a real sleeper, great bass, and good mids and highs, and relatively unknown for audio, used a lot in bands and PA.
A Yamaha P2200 would do nicely, 250W, big linear power supply, bi-polar output for good current and has magic Alps Black Beauty's as input level controls, feed your source direct in.
Cheers George