The above is excellent advice. I know from experience.ray_parkhurst wrote:Once you start doing focus stacking, especially if you increase in magnification, you will likely soon tire of the manual adjustments and will be looking for an automated solution. With respect to your statements about not wanting to go automated right away, I can only suggest to minimize your expenditures for the manual focus rail by buying an inexpensive one that will adequately do your initial work at 1:1 but doesn't offer the precision required for higher magnifications. I would still concentrate on getting a worm gear driven rail, rather than a rack and pinion type, since they are more precise, especially if they have a large-ish knob.
I wouldn't spend a lot of money on a manual rail, as one that's really precise and repeatable is going to approach or exceed the cost of something like a Wemacro.
At high magnifications, stacking with a manual rail is going to get VERY tedious. With a manual rail cheaper than a Wemacro, it's going to become maddening.
I used a cheap Chinese rail from eBay for a few years, mostly for single images. It was great for fine focusing for single shots. On those few occasions when I tried to do stacking with it, it was an exercise in frustration.
An alternative to (and an intermediate step towards) an automated rail is automated tethering software like DSLR Controller (for Canon and Android). The software is usually very reasonably priced, and allows you (with the appropriate autofocus lens) to do focus stacking with an inexpensive rail or no rail at all. There are a number of such apps, for PCs (Windows, Linux, and Apple), and for phones and tablets (Android and iPhone).
If it were me, I wouldn't spend more than about $50usd on a manual rail. I'd buy tethering software and save my money for a Wemacro or Stackshot.