You can find cheaper third-party light kits, but they tend to be dimmer and don't integrate directly with the remote and Boosted app. If you ride at night often, the Beams are worth the money.
Good luck finding Beams, though. With Boosted bankrupt — its patents sold to Lime and Last Mile SF (now rebranded as Boosted USA) only selling Boosted's leftover inventory — the only way to get Beams is to pay a markup for it via a third-party seller or buy it used. Another thing to note: there's no promise the Beams will work with the last version of the Boosted app since it's no longer being developed. Buy with caution.