Amazon offers Prime members Riddick: The Complete Collection on Blu-ray
with free shipping
. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it adds $4.98.) That's the lowest total price we could find by $10. This 3-disc set includes Pitch Black, The Chronicles of Riddick: Dark Fury, The Chronicles of Riddick, Riddick, special features, and digital copies of all films.
Note: It's currently on backorder, but can still be purchased at this price for delivery when available.