If you’ve got $4,000 then whatever you buy spend $3,000 and keep $1,000 on hand for maintenance, repairs, and reconditioning. You don’t get a car for $4,000 that is in perfect shape. People sell cars because they don’t want to fix something. Your job is to figure out what needs attention and deal with it. Brakes, tires, struts, etc are all good things to replace. Get the car inspected to be sure the motor, transmission, and drive train are all solid. You’ll need the $1,000 for something; new exhaust, tires, struts, brakes, motor mounts, transmission mounts, something.