Just today I also finished this exciting project, a camera rail for the GoPro action camera.
You can download the STL-file here: http://www.thingiverse.com/thing:77377
At Igus I bought the following things (about 63€):
- WS-10-40 – rail – 600mm length
- WW-10-40-10 – slider
To mount the camera onto the slider I use the CB2.7 ball head from Cullmann.
In order to mount the rail onto a tripod I use the CX470 camera plate, also from Cullmann.
Both mounts together cost around 20€.