It is a bit of an odd layout...the traditional RB50 style (like a VW Westfalia) is the most popular. Chevys are worth less than Fords (Harder to 4x4 them and not much aftermarket support) and the stripe kit makes it look dated. Needing a bit of cleaning and cosmetic work along with the broken AC, I'd say Brian W's evaluation is pretty accurate.
Also just to warn you, most appraisers won't have a clue with these vehicles. They might price it with conversion vans and value it too low, or they might value it with the Ford 4x4 Sportsmobiles and value it way too high.
Search the classifieds here for "Chevy" or "GMC" and you'll see some similar vans.
It's in pretty good shape for its age and mileage though. Best of luck with the sale!