I just bought the
Neewer Pro 4 Way Macro Focusing Rail Slider for around $45. It's made of aluminum and plastic, and is pretty lightweight. So far, I haven't had a chance to use it due to incessant rains.
However, my first impression is that although a nifty tool for the price, quality is going to be a letdown. When I mount my Canon 70D on it with a small metal lens or a big plastic one, the longitudinal slider rack does not mesh with the pinion worm, as its base tends to lift a bit from the rear, making the screw slip. However, this can be remedied easily by supporting the camera / lens a little bit from below while turning the thumbscrew. The latitudinal slider does not have this problem in the portrait orientation, at least.
I am not sure if there will be some creeping of the slider when a heavy assembly is mounted on top, when pointing down. The lock screws are quite flimsy.
Anyway, for the money, I think I'm going to get good macro shots where I was struggling with movement of my arms earlier. I might also need to buy a tripod with an articulating centre column and legs that go flat, and probably a sturdy ball head as well. I spotted a used set somewhere for less than $200, but I don't know if it's still available... :-/