PC on Sundering bow string please?

I just got a sundering bow string mod it's..

Sundering Bow String
-Armor Penetration + 20% (19% chance)

and j/w how much would i have to pay for a perfect 20/20??

thx guys i need help <33 much love

uh hate to bump my own thread but can someone plz gimme a pc on that? :/ and btw i saw somebody trying to sell a 20% sundering, 19% chance string just like mine for 10k ... is that about right?