They're out there...
Welcome to the Forums! Sorry about the back.. Many of us have bonked the back at some point in life.. Hope yours gets better..
As for Airstream motorhomes, there are two separate generations.. The Vintage units were built in the 80's to early 90's in lengths from 20' out to 34' using various chassis and aluminum bodies. In the mid-90's Airstream started building larger boxy style motorhomes, up to and including diesel pushers.
There are sub-forums here for messages about motorhomes, and a number are listed in the classifieds from time to time.. Any motor vehicle that is 15 to 20+ years old is going to have potential "issues", and most happy owners are either mechanically handy or have a good and trusted mechanic. IN addition to Airstream brand, Airstream also made Argosy motorhomes, with similar bodies and painted exteriors (including a few steel shell pieces..). These are generally less expensive, have less elegant intereiors, but share similar running gear.
It's hard to define a "fair price" for an older motorhome, as some have been thoroughly restored, with new mechanicals and flooring and lumbing and fabrics, etc, while others may have been sitting in a barn for 15 years and need lots of work.. Patience and a knowledgeable friend would go a long way in finding a good one...
In Theory, there's no difference between Theory and Practice, but in Practice, there is usually a difference...