A great reference for vise and grinder stand ideas is this thread over on Garage Journal....hundreds of ideas.
Vise and Grinder stands. I'm looking for ideas on how to use several in limited space - The Garage Journal Board
I bought a couple of dozer sprockets at the local scrap yard (105lbs each) that I'm going to weld together, then weld an I-beam vertically and finish with a heavy flat plate to bolt a really big vise on. The vise is too tall to put on a normal bench, so it has to be on a dedicated bench, or stand built to the correct height. I plan to add a set of wheels on the back so I can tip it onto the wheels and roll it wherever I want. The vise is 200lbs, the stand will be at least 300lbs, so I think it's going to be pretty solid.
The local scrap yard had a bin of semi-truck brake drums that are a popular choice for a base...some folks fill them with concrete as I recall.
Here's the vise...a Wilton C3 which has 6" jaws, pipe jaws, and weighs right at 200lbs: