Car crash help what to do ?

hello so my friend got into a car crash in the school parking lot and the person doesn't want to get the insurance into it because its going to sky rocket his so the guy said hes going to pay my friend cash. The damage is about 450. so what should my friend do ??? cant they go to the bank or something and get an official note saying the guy has to pay 450 by some time if not my friend can sue him ?? thanks