I guess that's a bit academic. Not just price I imagine. It had to be fit-able, powerful "enough" and reliable.
The modular 4.6 fits that bill and is strong as an ox. Powered not only Mustangs but Crown Victoria's, cop-cars, taxis and pickups. In the US 400k miles is common and over 1/2 million miles is not unheard off. Mine is over 210k miles and still going strong; sweet as a nut.
... wrong choice? Not in my book. I'm happy as Larry with my 'Olive'. Aren't you with yours?
David