Estimated grade. Sold by Bowers & Ruddy Oct '82 price realized $44,000. Lot #911.
Ron Guth: The official mintage of the Proof 1864 Double Eagle is 50 pieces. However, the number of surviving examples is probably less than a dozen. Since 1982, only 16 examples have appeared at auction, but there are number of duplications included there. Akers' observation that this date is "more often available than any other proofs prior to 1881" was reasonably accurate, but today's PCGS Population Report shows a couple of dates in the 1870s that have higher pops than the 1864. Among the Type One Double Eagles, the 1864 Proof has the highest population, but only by a single example. Regardless of the accuracy of past, present, and even future observations, there is no question that the 1864 Proof $20 is a rare coin, indeed.
Most of the examples certified by PCGS are Cameos, and the typical grade seems to be PR64. PCGS has not graded any Deep Cameo Proof 1864 Double Eagles.
The price history for this date in Proof condition is quite impressive, advancing almost ten-fold since the mid-1980s.
Greenwich Collection - Heritage 8/2004:7684, $123,625 - Bowers & Merena 4/2005:2339 (as PCGS PR64CAM), $143,750 - Ohringer Family Trust Holdings - Goldbergs 9/2008:1288 (as PCGS PR64CAM), $161,000