Sounds like your in the same boat as many... Here is your solution!
Buy a regular grinder (uses electricity not air powered) and go to Home Depot. They sell Norton brand and Norton makes a course type sander/stripper. It will strip paint, bondo, rust, etc. Here is a link to them: http://www.nortonautomotive.com/bear...pid-strip.aspx
They will not heat up and warp the metal and will strip quicker than 80 grit sandpaper. They also flex and will get in door jambs and trunk lids.
They make them in 4 inch, 8 inch and smaller for drills and grinders. Home Depot sells them for about $9 and some change. As far as how many you need I am not sure, they will last quite a while. I would start off with 2 or 3 and see how you like them first. They will not strip the entire car in a day but will cut down your time compared to 80 grit sanding tremendously!
Good luck!