From pp82/83 of chapter 9 of:
The Arsenal of Democracy: FDR, Detroit, and an Epic Quest to Arm an America at War by A.J. Baime
(Quote)
[.....]
Four days later, just before midnight, an armored car pulled up to Gate 4 of
the Rouge. Two soldiers unloaded top-secret blueprints for the Rolls-Royce
Merlin aircraft engine, the British-designed power plant that was the jewel of the
Royal Air Force. Following the blueprints, the Fords received the aircraft engine
itself. Knudsen arrived in Dearborn from Washington to help study the project.
On June 13(1940), Edsel returned to Washington with Sorensen to finalize the deal.
They arrived at 8:30 AM and headed to the Mayflower Hotel for breakfast.
Knudsen met them there. All talk was of aviation engines—the scintillating
technical challenge of producing them en masse, according to automobile
manufacturing principles.
Edsel appeared tired that morning. Not long before, he had checked himself
into Henry Ford Hospital with crippling stomach pain; doctors had run
uncomfortable tests, making him imbibe barium solutions and forcing tubes
down his throat. They were unable to diagnose anything. "I was concerned about
Edsel," Sorensen later remembered. "The doctors were keeping tabs on him. . . .
When he showed signs of indigestion, from which he suffered a great deal, his
father would be impatient about that. He would criticize Edsel unmercifully."
In Washington, Edsel and Sorensen negotiated a contract for 9,000 RollsRoyce Merlin aircraft engines. Six thousand would go to the British, and the
other 3,000 to the US military. The government would pay Ford a provisional
price of $16,000 per engine (about $10 per horsepower). Edsel kept his father
abreast of negotiations by phone, carefully explaining the situation so as not to
upset him. To Edsel's amazement, he was able to convince his father that the
family should take on the project. As Sorensen later wrote in his diary: "I am
surprised . . . Henry Ford had stated that he would not make any war supplies for
any foreign nation. . . . No one could have been more careful in keeping him
fully informed than Edsel and I had been."
[.....]
(Unquote)
Shortly after Henry Ford changed his mind and backed out of the project.
The Merlin went on to be produced by Packard.
I have no cost figures for the Packard Merlin, but I imagine that it would be for an amount similar to what was offered Ford, for an equivalent production run.