Steve2112: look, I'm going to go out on a limb and advise you to go up and personally look over that unit. It probably has a 460 in it which is a sound motor as long as you don't mind getting the exhaust manifold bolts fixed, as they almost all had problems there. The C6 tranny (I think it's a C6) is solid, of course, that one may need servicing. It soooo much depends on how many owners and if anyone has recent receipts, say the last 5 years. You could have 8-10 yr old tires which is an easy $1200, leaking shocks, a slipping tranny, rotted rubber lines, belts and hoses, hidden water damage, the old freon that needs to be converted, or, it could have much fresher mechanicals and proof of updating. Can't tell from the description. I also noticed no pictures of the interior ceiling or walls, look at all the corners, around all the vents, under the windows and of course, open the benches up to expose the water tank to look for plumbing leaks.
You must, must get a knowledgable rv tech to inspect the rv systems and a trusted mechanic to look over the chassis. Figure on $200 in inspections, but that might save you thousands...
However, if it seems to check out and there's no water damage/rot, go ahead and offer like $3500 (presuming everything works, I mean everything) and the tires are not dry rotted. Do you want to always be wondering what owing an older class c would have been like? Go ahead.
I don't know your financial state but the old POS I bought was 8,000 and I sold it for $3000 after rebuilding the front overhang due to dry rot and finding out it fouled plugs every couple or three hundred miles due to bad rings. So I put fresh plugs in it just before I sold it... Ahem...
Anyway, if you like it and it passes inspections, give it a whirl. If it turns out to be ok, fine. If it doesn't, take the loss and peddle it. You will at least have had the experience.
Figure 8 mpg with a 460...