Sale 1:

Sold for 21 keys + Spec. KS Festive Black Box (1)

No B/O’s on outpost.

Seller: https://backpack.tf/profiles/76561198088878793#!/compare/1497312000/1497398400

Buyer: https://backpack.tf/profiles/76561197990037025#!/compare/1497225600/1497312000

X = 22

Sale 2:

Sold for 18 keys

http://www.tf2outpost.com/trade/28853099 - B/O of 18

Seller: https://backpack.tf/profiles/76561198107520045#!/compare/1493251200/1493337600

Buyer: https://backpack.tf/profiles/76561198091949595#!/compare/1493251200/1493337600

Seller’s link shows 16, but two were spent on the backpack higher above the keys in the link:

https://backpack.tf/profiles/76561198136465159#!/compare/1493164800/1493337600

http://i.imgur.com/0hn0YXd.png (these two keys)

X = 18

Sale 3:

Bulk for Vivid Noble

Seller: https://backpack.tf/profiles/76561197990037025#!/compare/1497830400/1497916800

Buyer: https://backpack.tf/profiles/76561197993989727#!/compare/1497830400/1497916800

Sale 4:

Bulk for Unusual Rocket Launcher

Seller: https://backpack.tf/profiles/76561198091949595#!/compare/1493856000/1494115200

Buyer: https://backpack.tf/profiles/76561198074924284#!/compare/1494028800/1494115200

Sellers:

22 keys:

http://i.imgur.com/nfNfltf.png - 4 days

https://backpack.tf/u/76561197993989727

http://www.tf2outpost.com/trade/29236836

24 keys:

http://i.imgur.com/QDi3LeN.png - 2 months

https://backpack.tf/u/76561198074924284

Sales at:

18

22

Going with 18-22.