UPDATE: The game is up on the PS Store and actually costs £14.99.
SCEE has revealed a list of the first budget PS3 Essentials titles that will be released for download from the EU PS Store later today, and Sonic Generations is one of them. Sonic’s 20th Anniversary game will be available at the cheap price of £15.99.00/€19.99/AU$24.95. Sonic Unleashed and SEGA Mega Drive Ultimate Collection have also been announced for the PS3 Essentials range, but it appears they will be coming at a later date. Gamers who prefer physical media will also be able to pick up PS3 Essentials games in stores.
Source: EU PS Blog