shoponkyo.com, wait for a good deal on a 507, hopefully around $250, Pickup a pair of es90 off ebay from the Harmon seller for $400. $650 is the lowest I can put together a 2 channel, full range system of any quality that you can easily expand into a 5.1 system in the future.
If you'll only ever want 2 channels, just get a pair of powered studio monitors and be done with it. The Behringer b2031A are supposed to be fabulously good for the money, but you're still only digging down to 50hz, so if you like electronic music or a 5-string bass, you really need to get closer to 35hz with bigger speakers or a subwoofer.