According to the website Julian included a link for above ...
"The car also has the dubious distinction of having been sold for over $1 million. The previous owner said that a good deal of the million, though, was in gems which, when received by the seller appraised for far less than their stated value, so this part of the car’s claim to fame is on rocky ground."
However, at this site, it lists the prices paid for the car at a series of auctions and $450K is the highest shown (although there are a couple of other known sales without prices associated ...
https://www.qv500.com/detomasoregistrypan01954.php