How much money would it take to go cross country?

Not sure if cross country is the right words. Me and a friend are half planning to visit each state (except Hawaii, and Alaska) in a row. If we do it it’ll be as cheap as possible. We’ll be camping out in the car. We plan on one week in each state tops. If we only use the car to get to each state and not for visiting places in the state how much would gas cost? What are some expenses besides food, and gas that I need to consider? Obviously this is just the beginning of me looking into it, but I want a little bit of an idea before I start really looking into it.