Matt Laur , Mar 01, 2009; 11:32 p.m.
The only 18-200 lens I'd consider would be Nikon's. Unfortunately, you probably won't find many of those in good shape used for $500 - just for the lens. If you want a rugged, weather-resistant DSLR, then look for a lightly used D200. They're getting pretty cheap these days. But the whole rig, in the way you've described it, isn't going to happen for $600, I'm afraid.