Due to this high production, most Bicentennial Quarters are not rare and are usually worth only their face value of 25 cents in circulated condition. Even in uncirculated condition or as part of special mint sets, they generally do not reach high values.
Coins in exceptionally high grades (e.g., MS-70 or Proof-70) can be worth more than their circulated counterparts but not to the extent of millions of dollars.
A limited number of 40% silver-clad Bicentennial Quarters were produced. These are worth more than the regular clad versions but typically only in the range of tens to potentially a few hundred dollars for coins in pristine condition.
Any Bicentennial Quarter with a mint error, such as a double strike or off-center error, could be more valuable. However, even the most valuable error coins in numismatic history do not approach the value you're mentioning.
Quarters that were part of special mint sets or first strikes might carry a premium.
The figure of $90 million you mentioned is extraordinarily high for any U.S. coin. For context, the most expensive coin ever sold is the 1933 Double Eagle, which fetched $18.9 million at auction in 2021.