OK - this is from the perspective of someone who hasn't built anything, but I have read loads. When I had some time to look at my potential router, I looked up and down the cost scale of every option I could find for the slides. The cheapest of all was drawer slides, but clearly not good enough.

It seems to me that you are on the path to re-invent the skate bearing on angle solution. You can see them all over the place. Here is just one example, albeit a crude one with the skate carriages riding on round rails - er pipes actually. Most examples ride on inverted angle.

With a set of 8 bearings at a fiver or less, this is pretty cheap and low friction.