I'm pretty sure you can't find anything that powerful for $20
I've got a really powerful green laser (beam is very bright and on a clear night travels at least 1km), and I got that for about £8.
It claims to be <1mW, which makes it legal to use and apparently safe (should it be fired at eyes the automatic response of closing your eyes should be quick enough to prevent damage).
HOWEVER, it's staggeringly powerful, and typically green lasers aren't as low power as this claims to be. Plus it came from a dubious ebay seller and the electronics are not of the highest quality.
So, I would believe that if it were to be tested it would not be legal to use. So I make damn sure not to point it at people, animals, buildings or the sky if I even suspect there's aircraft up there.
You should follow these rules with all lasers anyway. But you can get cheap, possibly bootleg lasers online. So it's worth it to check the laws first.
Also, avoid blue lasers. They usually are dangerously powerful. Like, 'permanent eye damage' dangerous.
