Naomi, a fair price depends almost entirely on condition, not age.
At that price I would expect all the parts to be present and in their proper places, and no major structural issues with the shell, frame, or floor. There will likely be cosmetic issues, inside and out. It may require some mechanical or electrical
repair, but it shouldn't be too extensive at that price.
Here is a link to a very helpful resource from the document center: Fiberglass RV - Document Center - Buyers Check List
Welcome, and good luck with your search!