Have you looked into the big players? BH... Adorama... Itsupplies/Atlex? I notice if you buy 12 carts at Adorama at once, its a bit cheaper than at BH. ItSupplies/Atlex doesn't offer a package deal for all 12. The prices for the 330ml and 700ml seem to be consistent across the board, unless you go for 12 of the 700ml ones which is $50 cheaper at Adorama.
Heads up for iPF6400 users, the 300ml carts when you buy the package of 12 is actually $200 cheaper at Adorama, or $50 cheaper if you go for the 130ml carts.
The crappy thing of course is that colors like green and blue are hardly ever used, so maybe you buy the 12 cart package the first time, but no sense in buying it every time as you will never get to use up the colors that are used 1/3 as much as the most popular ones like GY or Y.