I also used a grinder with a fine grit flapper wheel which worked well. Using the fine grit wheel takes the bondo down quickly and doesn't dig to deep into the metal. But dust will fly and you will need to still use a wire wheel to get into the seams.

 

Not sure if Lowe's carries automotive stuff, but I don't think so. At least I have never seen any automotive products at places that specialize in home building products.