There were over 1 1/4 billion 1964 P and D quarter's minted. Out of all of those I suspect that only a couple thousand have been found with this reverse, and it could very easily be less than that.
PCGS shows a Population of 2387 total, of which 134 are FS-901. Of course, one can expect quite a few in unattributed slabs, so better just to cite their Price Guide. They quote a "normal" 1964-D in MS65 at $20, and FS-901 in MS65 at $500. The only MS65 example I found a sales record for hammered at nearly $1000 two years ago. If we assume yours at AU, it's still a ~$75 coin.
When I got it, I wasn't concerned about value, I spotted the variety and wanted it for my collection, having said that, I have way way less than $75 in it.
Hats off to @Hommer and @physics-fan3.14 for working out a disagreement and modeling such behavior for all of CT.