0
With the 1.6 engine, discard at or under .787".With the 1.8 or the 2.0 engine, discard at or under .866".
Both models of the Boeing 787 (787-8 and 787-9) can fly at Mach 0.89
The 787 prices:
787-8 = US$185.2 Million.
787-9 = US$218.1 Million.
787 = 787.0