Hi, there's lots of great info here. Sorry that this question has been asked so many time. I'm planning my epic three month roadtrip to thirteen national parks out West in September, but I don't have a car. There's lots of threads on renting vs. buying, but they're mainly by visitors to the USA under 25. I'm a 40-year-old US citizen, but I sold my car after moving to Boston. It would have come in handy now.
I did some calculations estimating the full cost of buying (insurance, title, emissions check, depreciation, etc.) and renting for three months. Budget Rent A Car is only $1,300 for a compact with unlimited mileage. After adding a non-owners liability policy (my credit card provides free collision), this is actually a bit less than buying and selling when I'm done. And there will be no worries about maintenance with a rental car. Also there's no inconvenience of having to find, test drive, and sell a car.
It seems like renting is the way to go then. Am I missing something? I guess the thing that makes me hesitate is it would be nice to be able to sleep in the vehicle. Motels and campgrounds will get expensive for one person over three months. It would be nice to have a van I could sleep in.