Roller supports are handy items to have around the workshop or the job site, and like C-clamps you can never have too many of them. Unfortunately, they are not cheap. To make some lowbudget versions, I use plastic drainpipe offcuts screwed to wooden uprights. Then I clamp them to sawhorse crossbars at the desired height.
As shown in the drawing, I use a piece of pipe that has been cut in half lengthwise for the sliding surface of the support. For 3-in. pipe, a 2x upright will do. For smaller pipe, use 1x stock. Affix the pipe to the upright with countersunk flathead screws. In use, the plastic pipe offers very little resistance to a piece of stock sliding across it, and it will even allow a piece of stock with some sag in it to climb the curved surface.
Bob VonDrachek, Missoula, MT