From his national best selling book, The Fifties David Halberstam estimated the price tag for Le Sabre at "roughly $7-million dollars." Read Mr. Halberstam's exact quote in the second paragraph directly below. 

The seal of proof establishing how the LE SABRE is the most expensive automobile ever made (in the world) is practically etched in stone within the annals of Detroit's modern auto history. While doing a deep probing historiography, one comes to realize that facts sometimes lay buried under the surface, or in this case "covered in a shroud of secrecy" for decades of time. This goes double around a story surrounding a man and his accomplishment that is perhaps unparalleled. Until now, nobody had ever before done the due diligence and put this entire story together behind the man who, among other things, created not only the first automobile "design" monopoly (at GM) but also pushed it upwards towards becoming the world's largest, too. Many historical records and documentation at this website precisely chronicle the history behind Le Sabre and explain why this automobile cost such a tremendous amount valued in 1950 dollars.