Zavvi offers the Sylvester Stallone Collection on Blu-ray for $11.83 plus $1.44 for shipping. That's the lowest total price we could find by $5. It includes Cobra, Assassins, Tango and Cash, The Specialist, and Demolition Man. This set is region-free; the films themselves will play on US Blu-ray players, but the extras and special features may not.
Of note, new customers can cut the price to $10.65 via coupon code "WELCOME".