Seconded. Here in Austin, there are places which can service the old VWs... but in other areas, they are few and far between.
Plus, there are gotchas with the Rialta. The bathroom pulls forward on two handles/latches, and has a water pump just for it, if I remember right.
I'd probably would go for a less exotic, but a lot easier to service class C on an E-350/E-450 chassis. Just make sure the area around the cabover is not rotted away (pull away the mattress and look for discoloration or rot.)
For example, there was an '04 Minnie Winnie for sale in Bastrop for around 22k in decent shape. Another place to hit for deals would be PPL Motorhomes if you are near Texas.