The MP designers create and modify their bots based on what sales think that the market will tolerate. There is a common trend to inflate prices based on cheap accessories.

Sunstreaker appears to have a lot more parts than the other cars as well as a yellow deco which is a difficult color to match across materials. The more paint apps, materials and gang molds the higher the production cost.

I would expect it to be around 8 - 10, 000 jpy depending on how much paint they use.