I would tend to aggree, the trouble with Cat D's is that you just dont know. Its all guess work, and a lot of money to throw at a "Bargin" In my experiance there is no such thing as a free lunch. Plus if it was that greater a fix job, within such a short period of time why is he/she selling it??
I have also done a bit of home work on the price too for you, I have e-mailed you a copy of the PDSN report (electronic black Cap guide) and the rule of thumb for us, is you take the trade price and half it for a CAT D - Makes interseting reading