The amount they can sell it to you also determines the price, competition also determines the price.
For example, when I bought my car, $20,000 car I asked for an spare key, they said it would be $400, it came with 2 keys already, so 4% of the value of the car was the keys? I can buy an entire alarm system, installed for less than that with two controllers. The reason the cost is so high is because they have a monopoly on those keys, nobody else can make them.
The point is, just because you can buy that part, for cheaper doesn't mean that actually costs the manufacture less to produce, it might, but not necessarily.