whats this runestaff worth?

[Snoopy Dogg]

a 7x/4x acuity t5 ensorcelled runestaff with banshee flares?

[Filthy_Sanchez]

Hard to give an answer without knowing the magnitude of the flare.
If it's base banshee, probably not very much. +10 TD/DS on a flare chance in the script slot is a hard no for most people when OTS sigil staves are 1k bs.
If it's max banshee, I think a case can be made. Even then, I personally wouldn't trade +50 TD/DS on a flare chance for the benefits of even a T3 Sigil or similar.

[onurb]

This might help you here, its when it was last sold:

http://forum.gsplayers.com/showthread.php?137424-Banshee-Stick