Just spit-balling a few ideas:
1. I wonder if there's any power tool LED lights that could work. E.g. the DEWALT DCL060 LED worklight produces 1500 lumens and costs ~$100 (cheapest I found online was at IHL for $84). That polisport setup is great and all, but costs $477 from gnarlyparts
and claims 800 lumens. I don't think my wallet opens that far.
I realize the lumen rating isn't the whole story as the Dewalt light is probably a floodlight vs. a more focused headlight, but still. That presumes you don't also have to buy a battery (although still cheaper if you do and you could use it for other things). The DCL060 looks a little bulky, so maybe that's a bad example. Maybe another brand makes something slimmer. You could use the light for other things, take it camping etc.
2. Lots of LED lights have variable input voltage ratings. E.g. this $150 LED light bar from Princess Auto reads 10-30v and claims 5000 lumens:
https://www.princessauto.com/en/detail/ ... -p8604035e. I wonder if you could figure out a way to power it with an 18v power tool battery (I don't actually know if that's safe since I think power tools have some sort of protection against discharging them too far). Maybe someone clever like Axel99 could invent something to market to us...
3. I have an LED headlight I can mount on my helmet for night riding that's powered by a regular old 12volt lead-acid battery pack. I bought the light first and then went looking for a way to power it. Investigated li-on and li-po RC batteries, but they are expensive and will also require a special charger.
I wandered into Battery World on Barlow and chatted with a fellow there about it. The guy said he could make me a custom Ni-cd battery for less than the lithium options, but that it probably wasn't worth it -it would only be a little lighter and smaller. They've got a bunch of small sealed lead acid battery packs there in lots of different shapes and sizes. The one I bought is slim, but fills about 1/3 of a hydropack and could power my 1500 lumen LED light for about 4hrs. In retrospect, it's still a little big and heavy for comfortable wearing, but I also don't need as much capacity as I bought. It cost $20. Next time I think I need to use my helmet light, I'll probably just go buy a smaller battery.
Those options presume you want a usable light for riding at night. If you're just trying to be legal, I don't think you need go even that far.