Here's some helpful links, but
Step 1 is
ALWAYS figuring out how much you can ACTUALLY tow. And the real life max towing capacity is much lower than the manufacture stated max towing amount.
How Much Trailer Can You Tow (Part 1)?
http://popupbackpacker.com/how-much-trailer-can-you-tow-part-1/
The 75 Percent Rule of Thumb
http://www.popupexplorer.com/?p=210
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Buying Used Camper Checklist
http://popuptimes.com/?p=750
How to Buy a Pop-Up Camper or Tent Trailer
http://www.popupportal.com/index.php?topic=31201.0
Purchasing a Used Pop-Up-Camper
http://title-3.com/BuyUsed.htm
Unfortunately, NADAGuides or similar pricing service can't help here. Condition is the ultimate factor in determining price on an old camper like that. It IS at a dealer so the price can definitely come down. Having said that, I would expect to do some work on a camper costing $1500. A good to go camp ready pup I'd expect to pay 3K or higher. That's just my experience in Texas. Your mileage may vary.
2011 Coleman Sun Valley, 1997 4Runner V6