I suspect if you want 'openbeam' (which is what adafruit sells) you don't have must option in terms of price.
Depending on what you want to do, you might go to woodworking specialty stores like Rockler or Woodcraft to look at their supplies for building jigs and t-tracks. Last night my jig for my wood router got broken, and I need to rebuild it, and I might be going with t-tracks instead of DYI drilling holes, etc.
Another way to make tracks is layer several pieces of wood/metal/etc. so that the bottom layer is solid, the middle layer has enough space for the t flange, and the top layer is thin enough for the screw post, but not for the flange to come out. My table saw had tracks that were wider than my other tracks, and I made my own posts with screws and washers. If you have a router setup, you can get router bits to cut the specific slot, but by the time you do that, you probably would exceed the cost of the adafruit pre-made parts.
I imagine if you go to toy stores, you might find tracks for toy cars like hot wheels.