Went to my local Costco and saw the 7-movie Marilyn Monroe boxset, "Forever Marilyn," on Blu-ray for $24.99.
This 7 Disc set includes the following films:
Disc 1: Gentlemen Prefer Blondes
Disc 2: How to Marry a Millionaire
Disc 3: River of No Return
Disc 4: There's No Business Like Show Business
Disc 5: The Seven Year Itch
Disc 6: Some Like it Hot
Disc 7: The Misfits
At $24.99, this comes out to roughly $3.57 per movie (sales tax excluded), and is more than 50% off of Amazon's current price ($54.57 as of this writing). I do not know if this item is available at all locations (or via internet) at this price, so YMMV.