Joe makes a very good point. The digital SLR has been around for long enough for a good second hand market to have emerged. The pro Nikon's that are mentioned are good for over 150,000 shutter actuations.
If I had my time again I would have purchased a pro Nikon sooner which would have allowed investment in better glass earlier.
Here are two examples different cameras but the same glass.
D2Hs (4Mpx) - built 2003
example
D2X (12Mpx) - built 2005
example