You can pick up a Crown XLS2502 for around $400 used, $650 new. I have one here that I use to drive a pair of passive subs, I've messed with it driving fullrange speakers and it sounds surprisingly good.
I've had 3.6Rs in a room that size and they're compromised by such a small space, but you already knew that. If you can get past the fact that you're not really hearing what they're truly capable of, then there's no reason why you can't enjoy what you're hearing.