I suggest you look at what living space you can arrange inside a van. What would be a Class B motorhome if someone built a house inside. Vans can be up-fitted with lifted suspensions, larger tires (but not always to floatation sizes) and 4WD. E-series/Econoline is the more popular for this, it has had a frame under it since 1975. Suspension mods are easier if you are not trying to deal with unit body construction and subframes of limited extent. Taking E-series to 4WD means using F-250 front end parts (a lot of the rest of E-250/E-350 is already F-250 of same vintage).
Problem with trying to do this with a Class C is that it can be difficult to gain much additional clearance. For many C models, much of the house and utilities hangs down below the chassis frame rails. The major exception would be excursion RVs, which were more often built on conventional cab 3/4 ton to 2 1/2 ton chassis, with the house built to clear pretty much what the chassis will clear.
You won't be finding excursion vehicles with houses on your budget, even the older ones from Tiger and from Frank Industries/Xcursion will be too recent, too much in demand.
One of the guys I work with in community theater is building his go anywhere RV on a 2.5 ton military 6x6 he picked up for about $800. His choice was a shop van body, as it is already insulated, has big windows, and forced air ventilation. That one might also run on just about any liquid that will burn.
Another low cost starting point for build-your-own on the house would be a box van or box truck. Truck is more likely to have larger wheels and tires, and thus greater ride height. Old U-Hauls are popular because of the lower floors, but that might work against you.
Tom Test
Itasca Spirit 29B