Sale 1:

Sold with ~1 key in skins for Peace Sign Caribbean Conqueror (22.5)

No outpost

Seller: http://backpack.tf/profiles/76561198179356497#!/compare/1473638400/1473724800

Buyer: http://backpack.tf/profiles/76561198051356793#!/compare/1473465600/1473638400

X = 22

Sale 2:

Sold for Terror-Watt Scotch Bonnet + 1 key

http://www.tf2outpost.com/trade/28409825 - B/O of 15.5, declined 14.5

Seller: http://backpack.tf/profiles/76561198066319618#!/compare/1471564800/1471651200

Buyer: http://backpack.tf/profiles/76561198148490379#!/compare/1471564800/1471651200

X = 16 (Capped by B/O, rounded up)

Sale 3:

Sold for Orbiting Fire Larrikin Robin

http://www.tf2outpost.com/trade/28429982 - B/O of 17

Seller: http://backpack.tf/profiles/76561198148490379#!/compare/1472688000/1472774400

Buyer: http://backpack.tf/profiles/76561198143145456#!/compare/1472688000/1472774400

X = 15

Sale 4:

Sold for Magnetic Hat Protector A Head Full of Hot Air (18.5) + 1 key

http://www.tf2outpost.com/trade/28472906 - B/O of 15, declined 14

Seller: http://backpack.tf/profiles/76561198058439196#!/compare/1473465600/1473552000

Buyer: http://backpack.tf/profiles/76561198179356497#!/compare/1473552000/1473638400

X = 15 (Capped by B/O)

Sale 5:

Sold for Aces High Allbrero (17.5)

http://www.tf2outpost.com/trade/28389914 - Deleted B/O

Seller: http://backpack.tf/profiles/76561197964171516#!/compare/1470787200/1470873600

Buyer: http://backpack.tf/profiles/76561198066319618#!/compare/1470873600/1470960000

The Allbrero, while in-date, has not been re-sold since this sale (which is at least a month ago). The current owner is now asking for 15 on the Allbrero:

http://i.imgur.com/2iyGMnE.png (I converted to imgur :D)

Going with 15 on this sale

X = 15

Sale 6:

Sold in about a day for 14 keys

No outpost

Seller: http://backpack.tf/profiles/76561198196583593#!/compare/1472774400/1472860800

Buyer: http://backpack.tf/profiles/76561198076912592#!/compare/1472688000/1472774400

X = 14

Sale 7:

Quicksold for 13 keys + <0.5 keys in items

http://www.tf2outpost.com/trade/28461104 - B/O of 14

Seller: http://backpack.tf/profiles/76561198143145456#!/compare/1472688000/1472774400

Buyer: http://backpack.tf/profiles/76561198196583593#!/compare/1472688000/1472774400

X = 13

Larrikin Robin Mini:

Sold for Corona Australis (10) + 4 keys in items + 1 key

http://www.tf2outpost.com/trade/28466756 - B/O of 15

Seller: http://backpack.tf/profiles/76561198291554347#!/compare/1473206400/1473292800

Buyer: http://backpack.tf/profiles/76561198128817586#!/compare/1473206400/1473292800

X = 15

Sellers:

16 keys:

http://i.imgur.com/qNgxEum.png

http://backpack.tf/u/76561198051356793

18 keys:

http://i.imgur.com/X9qtqYm.png

http://www.tf2outpost.com/trade/28484835

http://backpack.tf/u/76561198100722286

20 keys:

http://www.tf2outpost.com/trade/28384794 - 1 month

http://backpack.tf/u/76561198076020691

Sales at:

13

14

15 (3x)

16

22

Sales at 13 and 14 quicksold, excluding them

Sale at 21 is an outlier, especially with the seller at 20 keys going a month old

Going with 15-16