Given magic item creation rulings and staff creation rulings, I have some inquiries on how this might play out. I have found plenty of useful information from here before, so here goes nothing.
To make this staff, whatever spell effect that was made continuous would have the number of charges permanently reduced from the staff's total... This is just something I figured was right... anyway, lets put an example together.
(400 x 1 x 8) Magic Missle
+
(300 x 1 x 8)/3 Shield
= 4000 GP.
Tadah, we just made a Staff of Minor Arcana.
The tricky part comes next... Following magic item creation rules, the equation for making shield a continuous effect (Aka, it just happens as long as you wield the staff) comes out to be (1x8x2000)x2 = 32,000gp
I plugged in the staff's caster level instead of the required caster level of the spell out of principle. Simply adding the cost makes one of the most expensive paperweights ever with a total of 36,000GP of crafting cost.
However, if one were to follow staff creation rulings and instead add only 75% of the cost of shield (in this example) it would make it a slightly more reasonable crafting cost of 13,866 GP.
So at the end of this I have a staff the grants the wielder a constant shield effect while wielding it, has 9 charges, and fires magic missile for a crafting cost of 13,866 GP.... Or a really expensive Paperweight.
Besides not being a mad wizard, How should I solve this? Did I do this right, was there anything that I missed? Steps I should have taken instead? Which, if any, of these prices is correct? I wish to know so I may attempt to make something a little more functional.
Thank you.