I'd suggest checking the offer very carefully. Much to my surprise Apple's RAM upgrades on the latest Macbooks are very competitive with 3rd party suppliers.
8x2 GB memory with the Mac Pro: add USD 3,500.
Third party (xPCgear.com), Kingston KTA-MP800K2/4G 4GB kit 2x2GB, four kits: add USD 950 plus shipping.
I don't call that anywhere near competitive.
You can get a set of four 8 GB (2x4GB) kits for a bit more than 3,600, maxing out available memory slots, or very nearly a Nikon D700 and the 16 GB of RAM instead.