9ct/GB for plain BD-R is a rip-off. They cost 0.08 USD a piece (if you reach MOQ on Alibaba), plus about the same as patent license fees. So 16ct/25GB, not 9ct/GB.
Taking storage overhead (cases of some sort; spindles aren't well-suited to store BD long-tem) into account, the Chinese 20ct/50GB (plus patent; iirc sub-linear scaling with capacity?) option of a DL BD-R may easily be cheaper over all.
My costing put it as positive compared to disk even without massive discounts, but physical volume is a problem, and cheaply constructed disks are volatile.
Taking storage overhead (cases of some sort; spindles aren't well-suited to store BD long-tem) into account, the Chinese 20ct/50GB (plus patent; iirc sub-linear scaling with capacity?) option of a DL BD-R may easily be cheaper over all.