Your inquiries have been answered. Not long ago Greg Royar mentioned on this blog about a DIY DSLR bearing based slider he made. Here's the video explaining how it's all put together. Of course Greg does mention he's had some help from his Machine Shop to get everything a bit more accurate. Sounds like you'll all have to pressure Greg in pricing out a quote to get a few more of these things run off for sale. [Thanks Greg]
Details from the video:
The slider was built with some simple C-Channel aluminum acting as a rail, and the block is solid aluminum that's been ground down and bolted together. I picked up a box of replacement skateboard bearings from the local sports shop. The bearings were $8 for all 8. Right now I have the slider bolted onto a saw horse from home depot, but I'll probably be buying the popular fold away version so that I can get dolly shots from the ground.