Suggest you sign up for Proxibid.com (free) and follow the auctions for 99s like yours.
Set up guns like yours to "watch". Then wait till they sell, add in the buyers premium, typically 15-22% and see a real world value.
That will give you a range of prices that real buyers and real sellers made a deal at.
There is no shortage of 99s for sale on various auctions.
Good luck.