That is a good price. But I can understand how it could be that cheap- think about it, no Blu-Ray release means no disc, manual or box manufacturing costs, no getting stores to take copies/sell shipments to outlets so no hassle there, less tax (I doubt PSN games are VAT'd), then there's the fact that they wont lose any sales to preowned copies, or to defective discs, and since it is sold on PSN directly, no middle man like Amazon.com to take a hefty retailer's cut.

The only reason Prologue was so much was because the BR release couldn't be any cheaper, and to undercut it on PSN significantly would've made no sense as it'd kill the disc sales off. Makes you realise how much of GT5P was profit on PSN.