For posterity, I'll go into the selection process I went with.
Wacom seems to be the Apple of the pen tablet world: premium prices and a reputation for quality hardware that was perhaps more justified in the past. I first heard of pen tablets as 'Wacom tablets' back in the day. If the prices alone hadn't been enough to deter me, the Apple fan-type aura of elitism around Wacom would have sealed it.
I learned that pen tablets with screens have existed for some time. They are considerably more expensive than the older type, and likely less durable. I was also persuaded by arguments that drawing on the tablet while looking up at a monitor - while it does have more of a learning curve - is better ergonomically. Between these two factors I eliminated screen tablets from consideration.
There are different sizes - little portable ones that are very cheap, and huge professional ones that aren't. A medium is probably best for now; a drawing area a little less than the size of a standard sheet of paper.
Ultimately, I found myself drawn to XP-Pen, which seems to occupy a niche of affordable while still reliable. I found a used Deco Pro Medium, a model from 5 years ago, for an agreeable price, and it didn't take long to have it playing nice with GIMP. The pen doesn't need a battery, and the tablet uses a wired connection only. A nice thing is that neighboring buttons differentiate themselves with raised dash or dot so you can distinguish them without looking. There are cheaper models than the Deco Pro, but I was suckered in by it's scroll dial/touchpad. The dial seems like a nice quick way to zoom or change brush size, but I haven't yet mapped it to anything. I think I could be just as happy with a single button mapped to undo, but I'm still new to it and reserve the right to revise my thinking.
There seems to no shortage of people who buy pen tablets and never use them more than once, and put them up for sale, and most of those made in the past decade have the important bits: just fine tilt and pressure sensitivity, and perfectly good resolution. Chances are, a minimal one will serve you well and not set you back much, if you shop around.