Mark,
I'm no expert but I think you would be hard pressed to find many folks who would consider a 70's pop up as collectible.
I would say $1500 to $2000 would be a great price for you or $1000 to $1500 a great price for the buyer who wants to put some additional cash for repairs and then use the pop-up.
In looking through Southern California Craigslist the pop-ups are going for $1000 to $1800 for most with a few up to $3800 that are fairly new and in great condition.
Maybe this website can help you price it
http://www.vintagecampers.com/restorationinfo.php
