Restore to what condition?
It has been gutted, no RV furnishings. To just get it on the road as an empty shell, it could easily be $2000-5000 for good tires, brakes, suspension parts. At least it runs.
It could take $2000-3000 to furnish it minimally for use as some sort of a camping van, 50 to 200 hours work. Cost beyond that will depend on your standards of camping comfort, decisions about whether you need air conditioning, a generator for running the 120V AC systems (including air conditioning) when not hooked up, and so on, as the difference between a minimalist camping unit and full home comfort in a RV represents $10,000 to $15,000 worth of equipment. This is from experience building campers into van shells.
If you are talking about restoration to original configuration, museum quality or sale as a classic (there is some potential for this model) you might be looking at $50,000 to $200,000, and thousands of hours work, tracking down and buying OEM parts for a fairly rare vehicle, or having replica parts fabricated. This model is rare enough that the restoration task is closer to the restoration of a wrecked hulk of a limited production racing car, than it is to restoration of a 1950s-1980s mass production sedan or pony car.
"Restore" might be the wrong word, but if it is the right word, then lots of money and lots of time, the original purchase just a drop in a very large bucket.
Tom Test
Itasca Spirit 29B