D100's and D70's are getting to be pretty old stuff now. If you're looking for a pre-owned camera, I'd say get whatever is the more recent model in your price range. The new stuff is almost always better.
I haven't shopped prices since I bought my D60 a few years ago, but I image you might be able to scoop up one of those in your price range, given that it's been replaced with a newer entry level model. A D40 is nearly the same camera, but I don't think the kit lens is a VR (Vibration Reduction) lens like the D60.