I doubt the 302 3.5L V6 in the E350 cost $15k, the 402hp 4.7L V8 in the E550 cost $20k, and the 518hp 6.3L V8 in the E63 cost $40k.
You can buy a 412hp 5.0L V8 crate engine from Ford for $7.3k. A 550hp 5.4L supercharged V8 for $21k. Keep in mind that Ford makes a profit on these engines and are selling to the public at this price.
http://www.fordracingparts.com/crateengine/main.asp#mod
I'm separating the battery specifically because the electric motor
alone is already roughly the same cost as an ICE. If you tried to source a 300kW induction motor (akin to buying a crate engine from Ford), it would cost you at least $20k, and that's assuming you get a group buy at high volume (100+). The threads below show companies are charging $34k for a 150kW motor and $50k for a 300kW. With a 100+ unit bulk buy you can get the price down to $11k for a complete 150kW ACP system (with the PEM).
http://www.diyelectriccar.com/forums/showthread.php/looking-electric-motor-300kw-22718.html
http://www.diyelectriccar.com/forums/showthread.php/real-price-ac-propulsions-ac-150-28400p2.html
http://www.kleenspeed.com/ev-components/
The battery is akin to a gas tank and a gas tank does not cost $20k-$40k.