I got my Yamaha HS7's for 3400 NOK, which is about $500. They suit my needs very well, and I could probably have gone for the HS5's without losing too much. I tested them in the shop, and since I'm not very trained in listening, they sounded very much samey, though the HS7's did have a rounder, more full mid to my ears.
I've heard very good things about the Alesis Monitor One MKII. They are passive, though. So perhaps the active versions would cost you less, without suffering too much of a drawback in quality.
The word is, that you don't necessarily need the BEST, as long as you get used to what you have and can compensate for it. As long as the Frequency specter is as close to full as possible (20 - 22000 Hz) it shouldn't really be too much of a problem.
I've found the Yamaha HS5's on Amazon, new, for less than 200 each. If you go used, you should be able to save a few bucks too
http://www.amazon.com/Yamaha-HS5-Powere ... im_sbs_e_2Edit: I remember reading about the Fluid Audio F5, which is a VERY cheap alternative. About $200 for a pair. I have yet to talk to someone who owns them, but the internet is calling them decent. The bass slot helps to even out issues with the low end, something budget monitors often seem to suffer from. The F5's are the biggest and most expensive ones in the series, which means the entire line is done on the cheap. Their specs seem decent and so far, only the really elitist (sorry guys) people have criticized them to any significant extent.
http://www.fluidaudio.net/f5.htmlhttp://www.ebay.com/itm/Fluid-Audio-F5- ... 2ecc3aaae5