Thanks Del.
Concerning the SSD, the 768GB SSD can be created from these Samsung 830-based parts. Prices are from NewEgg.com
$190-220 256GB 2.5" SSD (in Apple's SSD stick form)
Model #: MZ-7PC256N/AM
Model #: MZ-7PC256B/WW
Model #: MZ-7PC256D/AM
$530-570 512GB 2.5" SSD (in 2.5" form)
Model #: MZ-7PC512D/AM
Model #: MZ-7PC512B/WW
Model #: MZ-7PC512N/AM
So the price plays between $720-790 of SSD parts. My guess is Apple gets a volume price of around $650 for the 768GB combination. They double that price for the BTO'd $1,300.
Apple could've gone with a more palatable 1024GB SSD (512GB stick + 512GB 2.5") and make $1,300 price tag seem very reasonable.