Nubster, I'm sure someone will chime in with the, "Duratrax = Duracrap" line, and while I'll admit that Duratrax isn't really known for their overall quality, I can easily think of worse rigs to consider. I have the Duratrax Evader BX which is an electric buggy I got for my 7 year old son and I have to admit, it's held up better than I expected. I don't know much about their nitro rigs, though, but I can say that none of the LHS' around me carry Duratrax parts, but I've had no problem finding them at places like Tower Hobbies and the parts are usually pretty cheap.
As to the particular rig you're looking at on eBay, there are two things that immediately jump out to me:
1. He mentions that the engine is easy to turn over by spinning the flywheel. That may be an indication that the pinch is gone from that mill and that it may be on its last legs. Just something to consider.
2. He has a $20.00 shipping charge listed. I would be more inclined to offer something in the neighborhood of $50.00 for the rig itself to bring your total to $70.00. $50.00 bucks, in my humble opinion, gives you a good, basic rig you can tinker with and build from.
Hopefully this helps somewhat.