There are reasons why these tires cost more, a lot of them. A big one is volume. How many stock production bikes out there run a 240/50VR-16? So many different bikes run their own unique sizes, cars, although there are also a lot of sizes, an 03 Honda accord LX uses a 205/65-15 all around, so does the 02 Toyota Camry LE. I don't know how many each of these were sold in the US alone but it's a hell of a lot more than the r3, multiplied by 4 when it comes to tire production and not 1.
Supposedly, there's more engineering involved in a motorcycle tire because of contact patch/hp and there are more compounds used which raises the price. Warehousing these things raises the price too, they aren't going to fire up a production line for one tire order, so they are going to do a run, warehouse them and wait for inventory to drop, but, since there aren't many bikes out there running this thing, the inventory sits there, costing more. Then when it gets low, the have to spin up the production line to stock it back up. Costing more.
If every motorcycle ran the same tire size, costs would probably be just above a car tire because no matter what you do, the volume will never be the same as cars.