I'm not sure there would be a large R&D side to the project. The mechanicals look relatively straightforward, and there is documentation of at least 1 homebuilt unit already, linked at the top of this thread.
And, on a related matter, a linear actuator is a relatively simple thing to build...even considering accuracy and backlash. Since imprecision is not cumulative, like on a gantry machine, the individual members could conceivably be less accurate, and consequently cheaper. (And, easier to homebuild, for someone without a complete metal shop in his garage) For reference, the guy whose site is linked above, got .002" resolution using allthread and hardware store angle iron, on his prototype unit. He's rebuilding it for much higher accuracy, but .002" is pretty darned good!
My concern is control...turning standardized coding into control sequences for one of these machines. Surely, since there are machines available commercially, *someone* has come up with a software library dealing their control. If not, this thing was designed in the slide-rule days...how hard could its control algorithms be to understand? :-)
The only real problem area for a homebuilder would probably be the ball joint. The ball joint requires a rather significant degree of freedom, and no backlash. One common solution I've seen on the attempted homebuilt units, is to use a universal joint. It would provide the level of precision necessary, but has all the grace and elegance of a baseball bat. Surely there is a better solution available. What we would need is the ball joint equivalent to Cranky's rollerblade bearings on gas pipe solution as linear bearings...it's the only really precision part we would need, and with 6 struts requiring one for each end, that's 12 ball joints for a single machine.
I just accessed McMaster-Carr's site, and they're not horribly expensive, but in this type of endeavor, cheaper is almost always better. These may be cheap enough, though I wonder about their accuracy?
http://www.mcmaster.com/catalog/109/html/1043.html
-- Chuck Knight