It probably wouldn't be worth it to go with OEM. You would have to take into account at minimum a new key fob, the push button, the plastic trim pieces for the dash, and all the sensors that go along with this system (passenger side, driver side, rear lift gate). You are looking at new handles for the passenger and driver side and the new tailgate trim with the cutout for the up/down functionality where the key hole is. This isn't even getting started with the electrical wiring wizardry for the sensors to communicate with the car.
I'm not sure if member BFLAN is still on here, but I believe he was the only one that attempted an aftermarket push start system on his truck. Take a look at his previous threads.