He's right - you usually get what you paid for. A runner that has everything working correctly and the right parts (no 12 volt conversions, no messed up wiring, no engine mods) should go for about $ 5000. If it has been taken down to the frame, sandblasted, engine rebuilt, new wiring, new glass, correct paint, new canvas, then you would be looking at over $ 10,000 - maybe more if the work was done by a restoration specialist instead of by the owner. The bottom line is that when you sell a vehicle, you find out that you are being paid about 5 cents per hour for your time.
If you like vehicle restoration, look for a vehicle that's all there but needs completion --- but if you want to just drive it and not fix it, then spend the extra up front.
M37s are still very common, but many of them were butchered by fire departments, city garages, and other end users. Parts are still very available, but buy new parts when you can, because the stock of new parts will become less and less. Keep extra spark plugs, points, a spare coil, a headlight or two, 24 volt bulbs, and other consumables on hand. When I used to have an M37, I kept an ammo box of spares under the passenger seat by the battery box. Things never fail in the garage - they fail somewhere away from any parts supply. If you have canvas instead of a hard cab, plan on brushing on coats of canvas waterproofing everry once in a while. Don't buy something high tech that's made for nylon tents, buy a product (Canvak) that's loaded with parrafin, mildew-cide, and some mineral spirits. That will do a great job. Canvak is even available with OD pigment in it as well.
When you need tires, the old MIL treads look nice, but they don't last very long when you drive on paved roads (asphalt roads are harder on the tires than concrete paving). Look for a more modern tire with a highway tread. It's not as original, but it's a lot easier to drive and the tires will last a lot longer. If you want to 100% restore it, then tire life won't matter - Wallace Wade tires in TX has correct MIL tires.