When I was laying out Andrewh's work bench, I picked up a sheet of 14 gauge steel. We cut it to size using an abrasive disc in a circular saw. We left enough overhang to fold it down over the sides. After that, we drilled small holes in it and used button head screws to hold the steel to the sides of the table.
That bench was made entirely out of reclaimed 2x6 lumber and is a BEAST. He'll have to try hard to kill it.

The abrasive disc in a circular saw works great on sheet steel if you keep the blade depth shallow. It cuts pretty fast.