When you address the underbody everything will be dependent on the size and offset of the four tires protruding into the air flow.
http://www.tacomaworld.com/forum/tir...155x70xR19.pnghttp://ecomodder.com/forum/showthrea...res-25208.html
I'd consider fitting BMW i3 tires (w/ appropriate wheels) with an offset such that they flush to the standard body panels. aerohead appreciates a round air intake at the stagnation point.
That Photochop was intended for a VW flat fourin front. With the stock Prius drivetrain it needn't be any bigger than this:
