I had a look at the NADA price guide and couldn't find any listings for Okanagan class B vans.
Here's some hits from googling Okanagan class b. Probably not much help.
http://www.uniqueautogear.com/unique_rv ... conversion
http://classifieds.castanet.net/showpro ... 70/cat/284
As Steve said, 25 years is going to be a long in the tooth class B.
I think you'll have to decide if you think it's worth the money, or whether you might
want to spend more to get something newer and potentially less problematic.
Or, it could be a reno project if you have the time, patience, skill, and money.
If the company that made them (Okanagan) is still around, you might try asking them
what they think, before you commit to anything.