I've posted pictures, hopefully pretty self explanatory. The pictures aren't exactly what I describe. Again, just what I was able to work up as an example given materials I already had available. One should be able to build one of these for under $20 in materials. Not really sure how much load this will hold and still roll easily. I put a hockey stick (it was close at hand) through it, placed it on the floor and pushed down pretty hard and it rolled easily. If more weight bearing capacity is desired, one might fill in the PEX rollers with something. I've been told that one can buy 3/8 OD fiberglass electric fence posts. Those would work well for filling the PEX.
Step 1: Materials
QTY 1 - 4" PVC toilet flange (hello easy mounting!)
QTY 1 - length of 3" PVC pipe
QTY 2 - Rings cut from 3" PVC fitting, doesn't matter what, buy one you can cut two rings from. (note, cap shown in photos as it is what I had) Actually, a cap might be good if the 'axle' doesn't happen to be 3", you can drill/cut an appropriately sized hole in the cap.
QTY 1 - 5' length of 3/8ID PEX tubing (I actually didn't have this, I paid something like $2 for it. It happens to be 1/2 OD)
QTY 2 -Some sort of rigid-ish plastic sheet like a binder cover, piece of plastic paneling, side of a rubbermaid tub, etc. (not in pictures, thought about this later - keeps assembly together)