Cost of a coin door = $100, which is probably around 7-10% of the cost of the cab. It's unnecessary, but so is this whole project. I would say go for it.
If, however, your budget simply can't accommodate a real coin door, don't mess around with a fake looking sticker. As soon as someone goes to use the coin door, and they find out it's a sticker, it takes away from the craftmanship of the cab.
Get a real one or nothing at all.