Hard question to answer. I have always owned older rigs. Each case is different. In Tires for example age often counts more than miles. Check the DOT dates on the side of the tires.
Engine condition (I assume a Diesel)can/should be evaluated by a professional.The brand dealers can do that or any reputable shop. Most manufacturers will check repair and maintainance records in thier computer system.
Price is between you and the seller. For me starting low and moving up is the best way. If you are set on that particular one you may be willing to go higher.
Try a bunch of sales web sites to get range.
The chassis can be checked by a Freightliner shop. Get a price on getting it up to your standards, or maybe they will find it is fine.
Nothing wrong with older MH but keep in mind that repairs are unavoidable and the odds should be figured in the price.
If it is local to you check for salt rust problems. I am in the Albany area and salt can be a nightmare in used vehicles.
Be sure to drive it, a lot.
Hope this helps.
2016 Bay Star Sport downsize from 2001 MountainAire
Toad GMC Terrain, might leave it home on some trips.