Price for a Flawed Crystal Ball

[Quatar]

My party aquired a "flawed crystal ball", which acts like a normal Crystal Ball except with the following addition:

flawed crystal ball (the subject of the scrying automatically notices the magical sensor created by the crystal ball)

Which in my opinion is a quite debilitating flaw, as it makes it nearly impossible to use it on enemies.
However it can still be used to keep track of party members and such.

So I'm not sure how to price it.
42,000 like the flawless version seems far to high at least.

[MrRed]

The Will-save DC for a Crystal Ball is pretty low (16)- so it's pretty unreliable to use on most enemies. I wouldnt cut the price too much- maybe to 3/4 or 2/3 of the full price.