This 1965 Riviera just sold for $302,500 @ the Mecum Auction on Saturday Jan 13. I was there - it was a very nice car.
https://www.mecum.com/lots/1098440/1965-buick-riviera-gs/?aa_id=515497-0
This 65 Riviera Custom sold for $77,000 - I didn't think it was that great - some flaws - IMO
https://www.mecum.com/lots/1107439/1965-buick-riviera-custom/?aa_id=524115-0
This one sold for $38,000 - I did not see this one
https://www.mecum.com/lots/1102788/1965-buick-riviera-gs/?aa_id=511456-0
There were also 4 1963 Rivieras which sold for between $8,000 and $51,700
Cheers all!