Of course the part will be expensive no matter what.
It's not hard to imagine it's all built in to the head unit, and only an sd card reader and a "key" chip inside the little plugin module to 'activate' the tomtom in the head unit.
Keeps costs down?
My 2004 Mazda3i and even the CX-5 lowest model, came with everything installed (cables/wires) for the fog lights when it didn't come with any.
I just had to buy the stock fog lights, plug them in, then swap out the light switch stalk and boom it works.
Game manufacturers make games and sell "unlock keys" as a downloadable content to unlock features they put on the disc. Game costs $60, DLC cost a couple bucks.
Would make sense for CX-5 costing thousands of dollars, and the gps plugin unit (a "key") be a couple hundred.
I don't have a CX-5 yet, so anyone who has one, since it's so easy to plug in the little unit, pop yours out and let us see what it looks like.
I would bet there's very very very very little electronics in it. Again just an SD card reader and some chips for a "key" and a board for all the plugs to go and relay to the HU.