This is a sketch from few months back showing how V-track might be a part of Contraptor. At that time, I looked at the prices of V-tracks and V-groove bearings and found them fairly expensive. Nevertheless I had ordered some material to build and test the prototype, and this weekend I finally got around to it.
Below are V-tracks that can attach to Contraptor angle or 1" T-slot. Fabricating wasn't too difficult but took some time. 3/16" holes were drilled in V-track at 2" intervals. 4" intervals could probably also work, but 2" fit nicely with 1ft and 2ft track lengths. One difficult thing was tapping small screw holes in the aluminum bar. I usually drill 1/8" hole and 6-32 screw self-taps into the hole with little effort. This works great in 1/8" thick aluminum. Here, the holes were about 3/8" deep and screws would stop dead after a certain point. I tried 6-32 tap in the power drill to save time and it broke on pull out after stopping too late. Basically the holes had to be tapped manually, advancing about quarter of a turn and then stepping back a couple of turns. Anyhow, this was only needed to be done once as they're not intended to be disassembled.
The V-bearing element still needs to be made. I only have 2 V-groove bearings from VXB.com and I'm trying to find them for a reasonable price (not $15 a piece). They are angular contact bearings so they can support combined loads and have very little axial play. The V-track + V-groove bearings with T-slot should be able to handle loads of a larger CNC machine - 1ft x 2ft and perhaps 2ft x 4ft.