I've seen homemade ones: Bottom was a sheet of plywood with a 2x4 cut about a foot long glued to the plywood, the 2x4 peice has a hole drilled into it which holds a 5.1" PVC pipe with a small notch in the top, immitating the above link free standing pole. These are used with an addition pole mounted in the floor as you see in the picture.
Anyone have any other ideas on how to make these? I need to make 4 of these. I'll also line the bottom with some type of soft cloth so the gym floor doesn't get scratched.