The D40x and D60 can use any nikon mount lens ever made, you just have to shoot manually (is that a bad thing?). They only "require" AF-S lenses if you shoot strictly auto everything. The D3000 and D5000 can use any Nikon mount ever made except for non-ai lenses, which can easily be modified. (I just bought a VERY nice performing lens for $18 off eBay today for my D60...)
I'd go with a a D40 or D40x, use the extra cash to buy lens or two. Maybe get a single AF-S lens and try out a cheap (price; not quality) manual focus lens or two. I feel like I've learned more shooting full manual than most people would shooting on auto for sure.
I got my camera from
Cameta Cameras off eBay. Be warned though that Nikon does not warranty products unless they're bought new from a preferred vendor. Anything second hand you're SOL for warranty purposes.
Best bet is to read, read, read, check the cameras out in person, read, read, read.
I have no experience with Canon cameras.