I can pretty much guarantee that kit is WAY cheaper than it would cost to put a decent set together yourself. Granted it doesn't use even close to the same number of LEDs as I did, but I'd guess I had about $150 just in parts, (super-bright LEDs were/are pretty expensive), plus the countless hours of labor.
As far as a wiring diagram, I don't have one. I just came up with it all in my head, and calculated resistor values based on the LED ratings, and assumes a 14V source.