At that age, it is really difficult to say how much a motorhome is worth, and when it has been sitting, what it takes to get one road ready. That also depends on how you plan to use it, occasional short trips or extended travel, and how reliable you expect it to be.
I know two people who bought motorhomes past the 30 year mark recently, both Winnebago, one an old 24 foot Brave, the other a 36 foot Chieftain. The Brave was $300, it runs well enough for 50-200 mile weekend trips, the house is structurally sound and doesn't leak, but the systems in the house are pretty much a rebuild or replace project. The Chieftain was $800 from an estate sale, it is in Good+ condition, everything works, it runs well enough for local trips, but for extended trips it should have new tires, suspension and brake work, and probably a cooling system flush, replacement of belts and hoses, and maybe a transmission service (fluid changes and adjustments).
My own MH is 11 years old, I've been using it locally, I replaced tires before my last extended trip ($1200 five years ago), repaired brakes two years ago ($800), but I would expect to spend another $1200-$2000 to get it ready for a long trip, because it has spent too much time sitting.
Depending on your budget for service or repairs, and how you want to use it, a price of FREE might be too high, because it could need $5000 or more worth of work. If the RV is in top shape for its age, and already in condition for extended travel, it just might be worth $2500, because that is about the floor price for motorhomes in really good usable and road ready condition.
Tom Test
Itasca Spirit 29B