Vudu has the Harry Potter Complete Collection (8 films) in HD for $55.99. Not 100% sure about regular pricing but I believe it is typically at least $40 more expensive for HD:
They also have individual titles on sale for $7.96 each if you don't need all of them.
iTunes has the collection for $59.99 (regular price $119.92, according to iTunes):
iTunes doesn't have original titles on sale.
For reference, the multi-format version on Amazon (Bluray + Digital HD) is currently $119.99.
There was a similar deal at the end of last year: