We avoided most of these, but here's a trick we used that actually worked pretty well.
We knew we wanted a few dolly shots, but getting those super nice dollies with track was expensive and difficult to work with, so instead, we rented the cheapest dolly they had. It was basically a furniture dolly with a handle on it, so DIYers out there, feel free to steal something from the garage and give it a handle add on till it looks like this:
Then we went to Home Depot and picked up one 4' x 8' particle board sheet.
It's perfectly smooth on one side, and the other is rough and grippy, which is perfect. Then we had the guy in the store cut them down to four separate one foot strips, and voila, you have 16 feet of track.
You line up one track under each wheel, then you stick another on the end of it and cover the seam with tape, and it works awfully well! The more weight you have on it and the tripod, the smoother it will be.
I don't want to oversell it, it's not the PERFECT dolly, and it's certainly no match for some of those ball bearings rigs, but if you need a length of track that's fairly decent and super cheap, I recommend this method.
As a side note, I actually rented something that was basically exactly like the Menacer shoulder stock except that it cost $100 for a week's rental. Boo.