At $9.00 per movie for the set (The Shagadelic Edition), I would go with Austin Powers and wait for a better price for North by Northwest...unless you don't mind paying $25.50 for NxNW. It's a much better film, but if you're patient and vigil, you can certainly get it for a much better price.
EDIT: Oh...and Hook 'Em Horns!!! (I miss living in Austin!)