Keep your eye on gumtree and ebay as they come up now and then. We've turned our Ex RAAF comms van into a full camper with slideout bed and all the mod cons.
If you are handy and can do work yourself you can pick up one relatively cheap and fix stuff up. Some come on the market after being privately owned since new but most have been used commercially and need TLC to bring them back to a decent standard.
Ours only had 70k on it when we bought it so they are around. Most are in the sub $30k region if the need work and clunkers that need a full rebuild in body and mechanicals can be much cheaper.
As they have a rigid chassis and are of unitary construction bodywise it is pretty simple to remove any existing body past the cab and build your own from there back.
