I don't know how much that 6.4 liter motor cost to build, but have you folks ever priced out a 6.4 crate motor from one of the performance mail order companies, like Summit Racing, or Jegs? I looked up the price of a 6.4 crate motor on Jegs website about six months ago. They charge $18,000 just for the crate motor. That doesn't include the drive gear like the alternator, air conditioning, etc. It doesn't include the air intake, exhaust, or computer system to run the motor.
2012 Ram 2500 Crew Cab 4x4: Cummins 6.7; 2" lift: 35s
2013 Wrangler Rubicon Unlimited: 6.4 Hemi; 3.5" lift; 35s
2014 Grand Cherokee Laredo: 3.6 Pentastar; stock; wife's Jeep