If $7K is your entire budget for the car, engine, interior, exterior, driveline, wheels, tires, etc. then you had better shop very carefully for a clean, rust free chassis. That, by itself, will cost you at least $2.5K. Wheels and tires will add another $1K. Getting the suspension and brakes back into a good stock condition will cost you another $1K. Cleaning up the interior and exterior will cost another $.5K.
That leaves you $2,000 to spend on engine, trans, diff, driveshaft, and halfshafts.