I am not sure I should say this as its a link to my project but https://www.indiegogo.com/projects/linu ... pberry-pi/
Unfortunately I think cnc on the raspberry pi is dead in the water as there is not really any interest, there are a few people that have looked at it but I think not enough to sustain community development and support.
I would suggest trying the beaglebone as I think there are at least 100 people playing with linuxcnc in that community whereas rpi cnc hackers can probably be counted on two hands.
Its possible things may change as there is not really much difference between rpi and beaglebone if you only using stepper motors. I am sort of using the indiegogo campaign as a market research tool, if more than 1000 people show interest I would try and work out some different or cheaper funding method in future.
If you support the indiegogo campaign maybe others will follow and I think unless 10,000 backers appear you will not actually have to pay anything.