Led tail light for 67 dart

You would think if they can charge 300 bucks for 2 bucks worth of parts it would be a priority.
It's easy to find schematics for LED's and they even tell you the exact resistance of the resistors and where to put them in the circuit depending on how many rows of LED's.
Then all it takes is setting up a board the shape of the inside of the lenses and solder it up.
I'd love to see one of you guys get 200 a set for building them.
How much should I expect to spend on one if you build it for me?