Try this- - - -go to a truck repair shop and ask them to sell (or give) you a discarded brake drum. Most 18-wheeler drums are cast iron, 16" in diameter and they weigh around 100 lbs. apiece. I'm in the process of building a forge from two of them, connected by a piece of 4" diameter black steel pipe. The bottom drum serves as a base, and the top will be lined with fire brick and refractory cement with a piece of 3/4" pipe through the middle with an air diffuser made from a pipe cap with several holes drilled in it. The air for the forge will come from a recycled electric leaf blower connected to the bottom of the 3/4" pipe.
A similar setup would work as your vise base, and it can be moved around the shop by tilting and rolling it. You'll need to weld a steel disc onto the upright and bolt it to the drum, as welding steel to cast iron is a real challenge.
Jerry
