Mage's Staff 12 lighting attack, -2 initiative, value: 28
Shadowbolt staff 6 attack, -6 initiative, value: 50
Two weapons found one turn one from the other, the first is extremely more valuable than the second, however it's value is only half.
At the beginning of the game many weapons have a value of 1-6, which is somewhat frustrating. Even later game weapons aren't worth the bother to carry and sell them.