Sorority has been officially released in the UK and US, and is now available to rent or buy on Amazon Prime Video.
Prices are as follows:
RENT £4.49 (HD) £3.49 (SD)
BUY £9.99 (HD) £7.99 (SD)
If you rent the film you get a 30 day period to start watching it, and then 48 hours to finish once started.