SEGA announced today the sale of a bunch of their iOS and Android titles for a limited time to celebrate Back to School.

In addition to Sonic CD, the other fine titles on sale for a limited time are:

Sonic the Hedgehog 4: Episode II – $4.99 (from $6.99)
Streets of Rage 2 & 3 – $0.99 (from $2.99)
Golden Axe™ 2 & 3 – $0.99 (from $2.99)
Gunstar Heroes – $0.99 (from $2.99)
Virtua Fighter 2 (iOS) – $0.99 (from $1.99)
Altered Beast – $0.99 (from $1.99)

source: SEGA PR