For what it's worth, I peeked at
TPG websites and Greysheet. Greysheet, of course, only goes to PF67, which was $7 bid. 1964 is its lowest price proof year for all Lincolns listed. PCGS says a PF70 would be worth $2250, with 4250 1964 proofs graded and only 10 at PF70. NGC has PF70 at $675 with 11+k graded and 0 PF70.
Stay well,
Diy89Nurm7