USA-4-Months Which car to buy?

Hi guys! I’m in the situation next Sunday to fly to Colorado and spend the next 4 months there. Since I’m only 21 the cheapest rental car would cost me 800€. Go GARNICHT! Since I’m also ami and want to increase my SSN (have so far only the ami pass) I would like to buy a cheap car. Type doesn’t matter…only no pick-up…….should not be quite old….ne have climate….and so around the 3000dollars…. I have times on the local car pages and there are already some nice offers……but I don’t have any experience how many miles are normal….which you should be aware of, or which dare you can buy without thinking even with many miles…….the dare only has to take me in Colorado Springs from a to b and fills a flight into the mountains……and have space for two bigger suitcases…… one of you can help me….^^… LG Thomas P.S.: Did jmd of you also vllt erfahru ng with purchase, registration and how it works with the insurance companies? I didn’t get any further. What’s such a liability per month? I really need an International Driver’s License and I have to specify when buying a car address or my social security number that I don’t have yet?……would be great if you could explain something to me …thanks