These kits range from $350 to $1000. Some kits offer different ranges of movement and features. Some offer only 90 degrees of movement others 130 degrees. I would recommend 130 degrees but it costs more. This can be an expensive mod but well worth it when you see the look on peoples faces. These kits are most affordable on ebay. Before you buy make sure you can install it or make sure you have already confirmed with a shop that they can do it.
Good luck!