No, buying a car, titling and registering it, getting it inspected, getting insurance, and then reselling it is not realistic, and a 1000 quid car may need major maintenance to be able to complete the trip. You may not be concepting a drive across the US fully - the UK is tiny in comparison. Generally, a person has to have a physical US address to be able to own a car here. Since 9/11, there is a lot more red tape involved in vehicle ownership than there was previously.