Variable speed for under $200 is going to be a very hard find. Standard 3450 RPM 8" grinders that have cast iron guards and are american made means looking through the Craig's List ads for a used one, or cheapest new is a JET brand made in Taiwan for 250$.
I'm in the same boat. I want a good 8". I might go the jet route. I picked this up last week at a pawn shop for 50$ but I still want a 8"
Craigslist hasn't produced anything in months of looking