CamonWheels is offering up some new V-Groove roller wheels for under $8 bucks shipped. Images show the grooved wheels fitting on 15mm rods, 1/4" rod, and 1" PVC. The overall OD of the wheel (outside diameter) is at 1". If you were to build a track dolly of sorts, the V-Groove or U-groove type wheels will help keep them on track.
A follow up video on the DIY Roller Bearing DSLR video camera slider. This is one that was posted about less than a week ago, and might give you some good ideas on crafting your own. It might not be suited for everyone, but you have to appreciate the effort put in to the instructional build info. [Thanks Sunny]