Another vote for Harbor Freight.
I bought mine years ago for $20, and I've used it to grind down (LOTS OF) welds, cut rusty bolts, cut out everything from rusty rocker panels to new .250 wall tubing, you name it.
The switch broke a while back, I just hot wired it so it comes on as soon as it's plugged in (gotta make sure it's not on the edge of the worktable when I do that).
The gears howl like crazy (even after regreasing), but the thing just won't quit, no matter how much I abuse it.