look at Bluebird Wanderlodges. Buybyebluebird and vintage birds are great places to get informed. They have big tankage & are a great value for the $.
I will say that an older RV is a constant labor of love. If you are not able to do the majority of your own maint & repairs you will spend a lot of $ on that. We have a 1987 Wanderlodge & love it. So I know what I am talking about. The other advantage to a Bluebird is an incredibly strong & knowledgable owners forum, Wanderlodge Owners Group. These folks have seen every possible problem with a Wanderlodge and are always ready to help with how to repair and parts location.
I will only say investigate all of your options carefully, ( you will need to join WOG in order to have full access but it is free and they don't give out your contact info to anyone ) Whatever you choose look for complete maint records. That will tell whether you are looking at a bus that has been lovingly cared for or neglected. A neglected, older unit can get real expensive real fast.