The milage isn't the concern. The overall age is the concern.
Assuming reasonable maintenance, the engine should be good for 150-250k miles. The big issue is you are looking at a 17yr old MH, which translates to around 2500miles per year. Most likely it sat for months at a time with no use. That means all the belts and gaskets had time to dry out. The oil had time to drain off the interior engine parts, did they really keep up on oil changes and other preventative maintenance? You need to be more concerned with the lack of use.
If you have a mechanic you trust, might be worth paying them $100-200 to look over the drivetrain and do a compression check. If it checks out, it will probably be fine...of course there are no guarantees.
The real issue driving the price down is the overall age of the unit. Is the roof in need of replacement, what about the air/con, fridge, furnace, etc... That's not to say you won't get 10-15yrs of use with minimal repairs but as it gets older, those repairs become more likely.
Also by that age, there is the keeping up with the jones factor. It will be obvious to anyone looking that it's a 17yr old MH, so people will not be willing to pay as much for it.
This is not meant to scare you off. Our 5th wheel is a 1997 and we expect to get at least another 5-10yrs out of her before selling. If we wanted to, we could keep her going indefinetly but at some point it makes more sense to trade up to something newer rather than put money into something older that has no resale value.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV