I've been pumping nothing but strength in an attempt to replicate the iron/tin turning into a copper short blade bug, and I've noticed that I just sold two copper greathammers (with fancy grips,) for $9. I've sold others for the correct amount, including one between the two that sold for less. Presumably they sold for $9 because it just completely ignored the hammer and only charged for the grip. One of the bugged ones was made the previous day, but I can't remember about the other.
I can't shake the feeling that it's all somehow tied to strength (specifically levels of strength that aren't multiples of 5,) but I'll get back to you if I can reproduce something reliabvly.