Welcome to the forum!
I think that you are going to be looking at used amps to hit that price point while getting the power that you want, which I'm assuming is 200W/channel minimum. I think that Emotiva will come the closest to that for a new unit, with the 200W x 3 XPA-3 costing $624 after shipping (temporarily out of stock). I don't recommend them, though, and I own two of their amps. Others here are really happy with them, however, so I'm mentioning them as an option.
I've read good things about Outlaw Audio and Carver's Cinema Grand line. There seem to be Cinema Grands (which are 200W x 5) on eBay fairly regularly, but I don't know if you'll be able to get one for $500 shipped. There's one that's in that range now, but the bidding is still going. I haven't tracked Outlaw Audio amps all that much, but I'm most familiar with seeing their 200W monoblocks go for sale used for about $225 apiece.