Auto body repair & detailing: Repair of small rusted dent on 1982 van, chevy van, professional repair

Question
I have a 1982 chevy van that was slightly dented a few years ago extending between the rear side window and the curve of the rear of the van.  It has now developed rust and I do not have the money to invest in professional repair.  I would like to ask the proper grit of sand paper and the proper aerosol version of primer to simply stop the rust now and prevent future rust since there is no paint to protect this area now.  I know to clean the area of any left over wax and to mask the area, but the area is approximately three inches wide and six inches long and must repair it myself.  The van may not be worth anything to many these days, but in this economy and loss of work hours, she is worth a lot to me.   Thank you.

Answer
JOSHUA.....SAND THE RUST OFF USING 180 GRIT AND FOLLOW WITH 220 OR 320. PRIMER CAN BE BOUGHT IN A SPRAY CAN AT THE LOCAL HARDWARE STORE. ANY AUTOMOTIVE PRIMER WILL DO FINE. APPLY PRIMER JUST TO COVER AND SPRAY 3 COATS WAITING 15 MINUTES BETWEEN COATS.