Welding tabletop

[turbotalon1g]

My wife and I constructed a workbench today, but I need to be able to weld on it, I was thinking about picking up a sheet of steel for the tabletop.

I couldn't find any at menards or home depot, so anyone have any ideas?

I am thinking discount steel, not sure where else to try and look.

tabletop is 3ft x 7ft

Also anyone have idea about thickness? I am thinking a 1/4" thick piece should do the trick.