My opinion, is to around the cost of an equivalent red laser diode. The diode itself is minute, very little material, and the rest of the diode package is identical. Now that these are being produced 'at scale' I see no reason why they should be more expensive than a red. The material in the actual diode is an insignificant part of the cost, and even if the manufacturing process is more complex, once the initial R&D is recouped, this doesn't add much to the cost.
The early diodes were so expensive for several reasons - patent bullshit and attempting to recoup initial investment costs - which are valid reasons. At first only one company was making them, so they could pretty much ask whatever price they wanted for them. At this point the demand for blurays outside of big volume drive makers is tiny, so individual diodes can still command a very high price - and a very handsome profit for the manufacturer.
Believe me, once bluray drives become more common these diodes are not going to be any more expensive than red ones.
(almosts starts drooling when thinking about this 
)
