All those inductors... Isn't there a cheaper way to drive those lights, e.g. using DC voltage+pwm?

Those inductors are cheaper than what PCBWay charged for making that wooden box, I don't think their cost matters much here.

Yes each LED channel has an inductor. I needed this because I wanted the LED to be constant current driven, to reduce flicker and improve their longevity

(and they cost like 5ct each)