A used minivan will often be cheaper, and you'll get more for your money, especially as 4 wheel drive often inflates the prices of used vehicles. A minivan actually also has more practical space for your situation, especially if you can remove one or both rows of rear seats. While you might not be able to fully stand, there would still be quite a bit more room to move than a SUV or wagon.
If you're thinking of keeping the car long term, that would easily be the most economical option. Cars are not disposable items, and there are always costs every time you buy/sell one. Of course, that's also a reason why buying a car just for a roadtrip usually is not the best idea. You can make pretty much any vehicle work for a roadtrip, but if you're going that route, you need to think just as much about what you need in a car for the next couple of years, not just the couple of months you'll be on the road.2. If I was renting a car, and it was the sort of car I really liked, it seems to me that I might as well just buy it and use it as my car in the future. I don't know exactly how the economics works out, but it isn't obvious to me that renting is more economical if I'm actually going to keep the road trip car as my permanent vehicle.