What machines are you using? Need some background as to what I'd recommend, etc. You say you're going to blast the car, inside and out. Where, equipment, recovery of media, where are you buying and what are you paying? Run away from H.F. supplying you medias, they are WAY too expensive. To do a car, unrecovering the media, better buy 1000 lbs at least of media. How big is your blast pot? You may be getting into areas/variables that weighing time, costs, supplies, local vendors, local providers of blasting services all needs to be weighed out.