[Youngster]

Sorry...forgot to mention...the saw stand has 3 legs, my floor isn't nice and level!! Youngster.

[Pete-3]

Just another thought (and then some) on the stand. I put the base (rim and pipe) together but I left the top plate off, then cut a short piece (8"+/-) of smaller pipe or tube to fit snugly inside, welded a plate on top, drilled a hole through both, inserted long bolt or piece of rod to keep it from turning during use. Mounted my vise. Worked fine, decided to build another plate for my small grinder. I eventually made 5 more bases and 4 of these top plates to work with different tools mounted . This way, the tools don't have to be mounted in one place where you have to keep going back and forth to. These also worked for me when I made a new top piece with a short piece of channel welded (flanges up) - taller jack stands. Put a complete '53 Rambler SW body 32" off the floor. Made it possible to put complete frame under and do extensive (suspension and floor) mods after that. Sturdy and strong enough that inside work could be done while needing space to work underneath also.

[Notorious]

For a great base, stop by a garage that works on heavy trucks and see if they have or will save you an old brake drum, the rears being the largest. They're routinely replaced for wear when doing brake jobs and only have scrap value when they're used up. I have an ancient (and pretty darned big) Blue Point bench grinder mounted atop a fixture with a truck drum as the base and it's no problem. No concrete fill necessary.
As far as putting wheels on something like this, I don't think you'd like it. I had my largest vise mounted on a very heavy-duty but wheeled work bench for a while and it sucked. I remounted it to a stationary work bench, much better.

[Chevrolet4x4s]

weld a plate to the side of the rim and then put casters on that when you need to move it tilt it back and when you set it backdown it wont roll away
Shane