There is the pre-purchase discount page, and I'll give it to you to be thorough.
However, right now, and possibly forever, it SEEMS that there has been a change in pricing for DLR, where the cost of buying the editable CD after you get home is UNDER the cost of that prepurchase page.
I'd suggest starting (or logging into an old) photopass account, and seeing what the pricing shows for you. I have old, no-pictures-anymore, photopass ID numbers from DLR on my account, and I see a price of 79.99 (I think) for buying a CD. It's possible (and I'm interested if it is!) that it's different for brand new photopass accounts, or for accounts that have old WDW photopass ID numbers on them...
So I'd definitely check that out first.
But just to be complete, this is the pre-purchase page:
http://www.disneyphotopass.com/previsitcdplan.aspx