To add to Len's comment, I've been watching sales of process lenses on eBay and there have been some real bargains lately.
But you have to be aware that process lenses usually cover somewhat -- sometimes a lot -- less than their focal lengths. To get an idea of coverage, visit http://www.schneiderkreuznach.com/archiv/archiv.htm for G-Clarons' coverage and http://www.galerie-photo.com/apo-pro...ikkors-en.html for Apo Nikkors' coverage. Dialyte type Apo Nikkors should have around the same coverage as equivalent Apo Artars and Apo Ronars.
You should also be aware that adapting a lens' cells to a standard shutter can be very expensive. Hanging a lens in front of a shutter can cost considerably less, at the cost (potentially) of inadequate coverage. Also large lenses (Compound #5, Ilex #5) are hard to find, not cheap, and have very limited top speeds (1/50 claimed, but they never actually go that fast).