You're probably going to need to be into something like these makes/models, but probably not at your price point.
Winnebago Flex BedI would think maybe an older smaller class C on an older Sprinter chassis (think early View/Navion) might be the closest thing to a class B in size, with a full sized bed. There are probably some older class B vans on Sprinters that might have longer beds. Class B vans are not the best fit for taller people, as they will tell you.
You might try one of the Class B Forums and pose your question there?
Class B Forum