Runestaff cost formula?

[RangerWickett]

I'm at work, and helping a friend stat out a character, and she wants a runestaff that can use mind blank and some other defensive/hiding magic. I don't actually know if I ever read the formula for determining how to cost these. Care to help me out?

 

[Pyrex]

Not that this is terribly helpful to you right now, but that formula *does* exist in the back of the Magic Item Compendium in the section explaining how Runestaffs work.