Earlier this year JuicedLink showed off an inexpensive roller bearing prototype slider design at NAB2011 with Olivia. Here's another video showing a bit more information. Sold with just a trollery and rail clamps, you'll be able to assemble your own slider at any length you choose. For longer runs another trolley block with roller bearings on each side keep the rails in position. The whole design is focused on keeping the costs down as much as possible. No word yet on pricing and availability, but other information can be found over at the JuicedLink blog.
Can't decide between a slider that 'just slides' or a slider with actual 'roller bearings'? (Technically, I guess that would make it a roller) There's a mix bag of shooters who prefer one over the other, but here's a new 'tweener. Glidetrack was teasing everyone with their new Hybrid camera slider a few weeks ago that uses a new hybrid Roller/Slider bearing, and it's now available to purchase online.
Looks like it's still based off of the IGUS Drylin rails with the new IGUS Hybrid bearings, but there's some custom work done on the actual carrier and adjustable legs. Obviously price is going to be pricier than the normal versions from Glidetrack. In fact, for the price of 1 single Glidetrack Hybrid you could almost score two Konova full roller bearing sliders of the same length. No descriptions on variable friction, but there is a hard brake stop to keep it locked down while moving around. If you're interested in hybrid designs, the Glidetrack Hybrid sliders / rollers are available in a variety of lengths from 20" (0.5m) - 78" (2m). You can find the prices below.