Amazon UK offers Back to the Future: 30th Anniversary Trilogy on Blu-ray Disc
for $14.60 (£11). Add it to your cart and proceed to checkout to drop it to $12.16
(£9.17). With $4.08
(£3.08) for shipping, that's the lowest total price we could find by $9, although we saw it for a buck less in May. It includes all three of the Back to the Future movies and includes deleted scenes and interviews with director Robert Zemeckis.
Of note, this item is eligible for the $1.32 (£1) movie credit promotion, listed here
This Blu-ray set is region-free; the movies themselves will play on US Blu-ray players, but the extras and special features may not.