Time for a fresh analysis of the 1906-D Half Dollar. David Akers wrote that the 1906-D was "considerably more rare with respect to population rarity than the 1906 P Mint issue" but more recent population data puts them almost equal in the number of coins certified of each date, with the 1906-P only slightly more plentiful in Mint State grades. Both the 1906-P and the 1906-D are approximately twice as common as the 1906-O and 1906-S. The real rarity of the four dates is the 1906-O, which has the smallest overall population in Mint State. However, the true condition-rarity of this group turns out to be the 1906-D, which has the fewest number of coins graded MS67 or better.
The single finest example of the 1906-D Half Dollar is a PCGS MS67 that sold in 2015 as part of the Eugene Garnder Collection for a record $47,000.