Then there's really low budget DIY'er way of going about this and that is with wood. Seen some contractors on a budget do that to used savana's they get. Someone buying a van for $10,000 or under might not have the cash for something from an upfitting company.
Maybe there's some platform you can buy that clears that area and leave storage room underneath? If not you can always fab up something of your own from wood. Just as long as you have access to the equipment or can pay for it.
If you're handy, you can most likely jimmy up a floating bed right above the wheels that you can fold up into the wall when not in use. But this is if you're handy which I am not. Those wheel bumps do take up a lot of space.