I'm not near you (in MT), but recently purchased a used 2005 Interstate in WI. An amazing RV!
A couple of thing's I'd recommend:
1. Check out NADAGuides.com for the ballpark market value of what you are interested in buying. $55K sounds kind of high, unless there are no miles on it. Use NADAGuides to negotiate.
2. More important, since the RV is in MN, take the RV to a local Airstream dealer and have it thoroughly checked out. It might cost you $200 for a bumper to bumper check (not the Mercedes stuff -- the van -- but the camper stuff). Be sure the camper was winterized correctly in MN. If not, it's expensive to fix.
Mine checked out on all levels, and I'm glad I had that confidence when I started out on a 10K mile road trip. And I got a good deal