Honestly I think about half to a third of the mod threads address this exact question.
I think it needs to be pretty big (no Jeeps of the CJ/YJ/TJ style and an Unlimited would blow the budget), exactly how big depends on what the driver is comfortable driving and how much people are willing to put on the roof.
Instead of starting with the vehicle, I would be more inclined to start with the mods, and see how much is left over at the end. I know it sounds backwards. I will make the assumption that camping essentials (tent, stove, etc.) don't get factored into the cost of the vehicle.
1. Refrigerator, probably about $1000 with all the necessary odds and ends, shipping and/or tax.
2. Storage, say $300 - $600 for something reasonably simple
3. Rack to store what ever doesn't fit in the car $500
4. Extraction equipment $700 for the entire Black Rat package including hand winch.
5. $500 for battery system and solar panels to power the refrigerator when the vehicle is off
7. I'm sure I'm forgetting a bunch of stuff, $2000
8. Repairs, maintenance and spare parts for the new rig $4000; sounds high, but when the dust settles, probably not far off. Christo Slee told me to factor than number into the price of any used FJZ80.
9. Tires $800. Tires are the things that make contact with the road, and without good ones, we are walking.
10. Auxiliary food and gas storage, either tanks or cans, or ???
So assuming the car really won't need most of the $4k I've allocated to repairs, we are looking for a rig in the, roughly $4,000 to $8,000 range that is reasonable size and has a history of being bullet proof. You can weed the options down further if you want common parts availability.
Based on that, I would be looking for (in no particular order):
- 98+ Isuzu Trooper. If you find one with a blown engine the are about $2-3k and a new engine (with warranty) is about $4k.
- Gen 2 4Runner
- FJ62 Land Cruiser, these can be had routinely for less than $4000 and cleaned up nicely for another $6000
- WD51 Pathfinder (90-95). Later models have frame problems, so inspect carefully
- 96-2000 Pathfinder, reliable and comfortable
- Jeep XJ, as new as possible
- Very early Tacoma, the 4 cylinder, regular cab 4x4 are relatively inexpensive compared with regular cab and/or V6
I did not consider GPS, onboard nav, lockers or aux. lighting as these can push the price up considerably and very quickly.