Hello Yewfren,
    Not with ball bearings per se, though I wonder if it might be easier to work with the wheel and axle of an old vehicle. If your structure is big or heavy, this might give you all the strength you need and be much cheaper to acquire. If it was from the rear wheel assembly of an older car, it should still have the steel break line used by the hand bread to manually activate the brake system, so you would also have a stopping mechanism. Then you could attach the axle (they are not that long, like a foot or so) to the the ground and build on the wheel, or if your structure was not that heavy, you could put the wheel on the ground and build on the axle (but this would make the brake impossible to use).
    For smaller projects you might also think of trying to mount onto a bicycle wheel, but I would not suggest it. Bicycles have very funky mounting systems designed to have an attachment on both sides. Instead try a wheel designed for a garden cart or wood card. They usually have 1/2 or 3/4 inch axles and are much easier to mount, you can just put the wheel over a piece of dowel and your good to go, though they often do not have ball bearings. With the usual caveats, Harbor Freight usually has an affordable selection of these kinds of carts, and sometimes just the wheels.
     As you can probably tell, I have put a bit of thought into this same concept... sorry if I am rambling.
    PyroCelt.

Speaking of cubes etc. I tried to make what I called the paralellogram of death, but the damned thing kept coming apart on me. Lots of fire (four seperate flames and the paralellogram is swung about the body in various moves many similiar to staff. Centrifigul force is quite powerful and I will need to become a welder before trying this again. I do have an idea of how to make it better after talking with someone who works in a machine shop. Keeping it light enough to spin, yet stong enough to stand on in the hard part. I tried it with wood and copper pipe.