It's all a game of relativity. This is more of a gun-attached-to-a-sticker than sticker-attached-to-a-gun value scenario, since skins w/ all of your pre-reqs (P250 Souvenir, FN, Metallic DDPAT) are worth around a key.

It looks like, as of late August, Holo NaVi Kato 14s are being bought at around $700. People seem to be defaulting to 5% of sticker price (per sticker) for valuation, but this isn't a skin that's highly valued.

3% sticker price (assuming $700) would net you a $21 valuation, 5% takes it all the way up to $35. Some middle ground in between those is likely going to be your selling price, unless you manage to get the attention of a DH2013 Souvenir collector who doesn't mind a modified souvenir skin.

Someone who's crazy for Kato 14 stickers might snag it hoping to make a profit down the line by selling it to other Kato '14-obsessed collectors who don't care about the skin's "purity."

tl;dr $20-$35 if you can find the right buyer, otherwise 7x market price for FN souvenirs.