Here is the one I built out of mostly flea market parts for, if I remember correctly, less than $25.00 and it does ride in the T-Track on my table. I have since modified it a bit, such as making the base longer so it will accept 8 inch wide stock and adding another clamp. I don't use it as intended, but mostly as a small parts holder to cut slots and miter joints in end grain for my boxes and clocks.
I also have the plan than John linked to and am seriously considering building it.
When something is advertised as being foolproof there is always a better class of fool that comes along to prove them wrong.