I think Buffalo nickels
semi-keys and keys are undervalued- 26S and 31S especially
I think 31S wheat cent is undervalued.
I think some of the Franklins in G-VG should be higher than buillion due to low mintages.
I think Walking Liberty Halves are about right- higher than buillion for most of the teens, 20s and 30s, buillion for the 40s. Keys are about right, maybe even a tad high. Peace dollar
set is low, considering the low mintage of many of the coins. At some point this set should routinely break $1000. Right now it runs $700-900 for medium to low grade sets.
I think Indian cents are undervalued, especially VG and better commons. But some of the early 70s and late 60s might be a little high.
I cannot believe one can buy Mercury dimes
for buillion, but I guess the massive mintages of the 40s dampens them from taking off. For them to take off, I think we are going to need a massive melt of the 40s.
Also undervalued, I think, are the semi-key Jefferson nickels
(38D &S, 39D&S, 42D). For coins that are >60 years old, this is remarkable to be able to pick up low grade for under $2 and yet one cannot get these dates (except very, very rarely) from circulation/roll hunting.