Pro amps are the only thing (new) that will fit that budget. The Behringer
EP1500 at $199 shipped is a whale of a deal. The A500 might be more appealing though as it doesn't have a cooling fan. I have the EP1500 and found it to be too noisy so I installed a
slower 24v fan - it can hardly be heard now and its only 10' from my sitting position. I use it to drive 2 DIY subs. It has more power than most speakers can use. Price for the quieter fan was $15 shipped and well worth it. The EP1500 never gets warm much less hot.
The cheapest 3 channel amp I know of is the Emotiva
XPA-3 but for $50 less I'd buy the
UPA-5.