apple's upgrade price is the same as buying a stick on newegg...which is about 630-650 bucks for a 2 gig dimm, I would just go through apple when you buy it if you can or just wait a while for the price of them to go down
OWC...$629.99. I think that's the best price you'll find from a trusted Mac-knowledgeable dealer. DMS is another great dealer, but their price is $671 right now.