You can order the LED strips from anywhere like Amazon. The thing is AP routes a channel is the roof of the cage so the lights are flush mounted and then they route the plug out the back top corner and make a channel on the outside of the roof for the plug wire to fit in so the whole thing is flush mounted. I personally would rather pay the $40 and have a nice clean recessed light in my cage as I don't have a whole router table set up in my garage lol.
As for doing it yourself, you could just have them route the channels and you order the lights and install them yourself. It really doesn't look that hard.