You know, sir, a very long time ago when I was young and green, I used to think that mintage--availability--of coins were a factor in their value. That is, the less that were made, the more valuable they were.
By the way, that's a good site to check out.
There were two in particular that always stymied me (and yes, I have them).
The first is the 1910 Barber half-dollar (Philadelphia mint).
The second is, or are, the 1950 and 1951 English penny.
These were extremely low mintages, but given the prices asked for them on the market, they might as well have been as common as 1964 five-cent pieces.
I still haven't figured that out. I suppose one can say, well, the Barber half-dollar (along with the Barber dime and Barber quarter-dollar) have never been popular collector's items, which drives down the value, but there's other Barber pieces with high mintages that are valued more than the 1910 half-dollar.
And as for the English pennies (the old half-dollar-sized copper pieces), there's a substantial number of British numismatists, and one thinks the rarity of those would command a much higher price than they do.
