I was wondering how much interest there would be if I provided a product for flashing the side markers with your turn signals that works with LED bulbs.
I would guess it would cost about $30 for one unit that will do two side markers (front or back). Circuit boards are the most cost and then shipping costs. The more boards I buy the less it cost me.
Price also depends on how the connections are made. Cheap would be you solder your own wire to holes (pads) on the circuit board.