I used to have a home studio before my house fire and went through many monitors. The Mackie HR824's were my favorite with the best quality out of the Events and KRK's I used. I paid $450 used for both. They had some dings on them but it didn't effect the quality of sound they produce. I'm currently rebuilding my studio piece by piece and as of now I'm using 2 Mackie SRM150's as monitors until I can afford the 824's agagin. Not exactly studio monitors but these things KICK MAJOR BUT and sounds superb. But if you're doing any mixing then I'd use headphones or regular house speaker since your the majority of people listen to music either thru headphones, car speakers or a little shelf stereo system speakers. I used Yamaha NS10's for the mix down.
Try Guitar Center's used section of their website. You'll find great deals on used monitors and will probably find the ones you listed in there. In fact I know I just some a couple of 824 and 624's going for some good prices on there. Hope this helped as with everyone elses advice.
Stringray club #398, Fender Jazz Club #365, Cort GB5, Sandberg VM-5, TCE RH750, RS-212