While it's true that R3 Harry Potter movies are way cheaper (now 350 each except Goblet which is 550), there are people who collects nothing but R1. For those, this piece of news might be worth noting:
According to Amazon.com, Warner Bros. has decided to put on moratorium all current Harry Potter DVDs in late 2006, early 2007. Disney style. No mention of how long (until HD version comes out?). The first three will go out of print 12/29/2006, while Goblet of fire will be OOP by 1/22/2007.
Also note that the R3 first Harry Potter (Sorcerer's Stone) is Fullscreen, so if you want widescreen, you might want to get the R1 version, before stocks runs out.