I’ve had fairly decent luck with ordinary dry-erase markers and the cheap Neje engraver (possibly 1W, maybe 1.5W, I don’t remember) that’s basically made out of old DVD-ROM stepper motors.
I actually wore out the laser after doing a few hundred caps, so I’m waiting for a new one in the post.
One of the bigger problems is predictable mounting so if you do 10 keys in a row, they’re aligned. A jig helps, like gluing a spare switch to the engraver bed.