Warner Bros. Shop is having a "Daylight Saving" sale this weekend with prices up to "70% off" ... you mileage will vary. Some of the newer stuff is still cheaper on amazon.
However, sort the list by price and then filter it by DVD or Blu-ray and you can easily look at the cheapest of items. (...and yes, some of them might not be worth that much)
There are a number of good DVD movies from $3.80 to $4.40 each.
Maverick DVD - $3.80
Rush Hour DVD - $3.80
Robin Hood - Prince of Thieves - $3.80
For Blu-Ray they seem to start at $9
These include the Blu-Ray versions of Harry Potter and Lord of the Rings though (and the side navigation lets you narrow your search down to specific franchises as well).
Free shipping on all DVD and Blu-ray orders.