I'm looking for a <10$ red rear light for cycling that's decent, either AA / AAA or rechargeable (for a non-LiIon friend). There are a few I'd found interesting
I use a P60 with a red XR-E dropin. Totally doesn’t fit what you asked for, but that what I prefer to use now. Previously I used the Planet Bike Superflash and the Radbot 1000.
I have and like both the Planet Bike Superflash and the Radbot 1000 that Sac02 mentions.
I don’t have the feeling that half-cheap bike taillights are a good use of money.
YMMV …
Most cyclists here use crappy blue 10-lumen 5mm led headlights that illuminate 2m in front of them (if anything) and similarly crappy 5mm led red lights. I figured there should be something that works better and is still cheap, 10$ is what he said he is willing to pay.
I'll maybe convince him to get either one of the two you mentioned
Remind him he’ll either pay once for rechargeable cells and charger (try the liitokala 20something, 2-cell USB charger)
or else pay over and over for alkalines until they leak and destroy the taillight.
Also — budgetlightforum overlaps a good bit with mtbr (mountain bike site) but a visit there and look into the taillight discussions would be useful.
And eliminate some recreational typing here since those folks have, exhaustively, discussed this for years.