Well if you DID go with a used Ninja 500, which would be the smartest choice, you probably don't have to worry about taking a hit on resale. There's a huge demand for those bikes used, which is why you don't see a lot of them. It's not unreasonable to think you could resell it for the same money you paid a year later, or close to it.
SV650 is again a better choice than a 00+ 600. And there's still a pretty good demand for those bikes in that price range .
If you're going with a CBR, you're going to be hard pressed to find a 2000 or newer for under $4K. Look at mid to later 90's.
Also, are you taking the MSF course? Buying riding gear? Take that into consideration with funds.
And if you're comfortable with it, you could always buy a bike on ebay, or at least use it as a measuring stick to find out what they're selling for.
Pick up a Want Ads, and if craiglist.com is big in your area there should be bikes listed.