Quoted from a few sources:

"Originally sold for the high sum of £1,150, it sold for $962,500 (£582,400) at Gooding & Company’s Pebble Beach classic car auction yesteday (Monday).

The 3-litre Bentley was first purchased by the car maker's first ever customer Noel Van Raalte.

Two were built as test mules, so the first production Bentley available for public sale bore chassis number 3.

Chassis number 3 is not only the oldest production Bentley, it may well be among the best preserved. It’s a “numbers matching” car that retains its original aluminum bodywork, all the more remarkable since the car was raced well into the 1940s."

• Original 1921 Bentley sells for over 500 times its original price – Investor
• Bentley's First Production Car Sells For $962,500 At Auction

1921 Bentley 3-litre Chassis Number 3 - Oldest Bentley in the world - YouTube

 

I understand that it sold for over 500 times it's original price, but considering that it was the first Bentley ever produced and sold to the public, I would have thought that it would have sold for much more than that. It didn't even fetch $1 million.