Has anyone considered using something like this as the stand for a 3 tier system? Inexpensive, but made of steel and each shelf is adjustable (removable?) and can hold up to 240 lbs. If you were to remove shelves 2 and 4 and stick 4 wheels on the bottom, you could be in pretty good shape.
Those things are pretty flimsy, we have a few at the shop and they really need to be braced to a wall or they move around quite a bit especially with some weight on them.
I think you're on to something. I spent way more constructing mine erector set style. Maybe it needs a little custom touch in the form of a sturdy base or some bracing.