Amazon has Harry Potter The Complete 8 Film Collection Blu-ray for $69.99. This is the complete collection in one boxed gift set.
If you need just the final film, you can pick up Harry Potter and the Deathly Hallows Part 2
Note: This is an Amazon deal. The price may change quickly.
Miranda Gydesen-Murphy via Facebook says
I wish Blu-ray didn’t cost so much more (yes I think $20 is much more) than DVD. We found 7.1 and 7.2 at Toys R Us today on DVD for $18 total – I was pretty excited