Sale 1:

Sold with 2 keys and a cheap item for Terror-Watt Herald's Helm (21.5)

No outpost

Seller: https://backpack.tf/profiles/76561198143320939#!/compare/1514851200/1514937600

Buyer: https://backpack.tf/profiles/76561198109871970#!/compare/1514851200/1514937600

X = 19

Sale 2:

Sold for Nuts n' Bolts Bomber's Bucket Hat + 1 key

http://www.tf2outpost.com/trade/29504706 - B/O of 18

Seller: https://backpack.tf/profiles/76561198011671663#!/compare/1514937600/1515024000

Buyer: https://backpack.tf/profiles/76561198173389367#!/compare/1514937600/1515024000

Bucket hat would be ~11 keys given these sales:

Sold for Dead Presidents Napper's Respite (Seller at ~10.5 for about a week)

Seller: https://backpack.tf/profiles/76561198011671663#!/compare/1515024000/1515110400

Buyer: https://backpack.tf/profiles/76561198225727252#!/compare/1514592000/1515110400

Sold with ~10 ref for Terror-Watt Respectless Robo-Glove (Seller at ~11 keys for nearly a month)

Seller: https://backpack.tf/profiles/76561198225727252#!/compare/1514592000/1515110400

Buyer: https://backpack.tf/profiles/76561198204099043#!/compare/1515024000/1515110400

This would make the sale around 12 keys, which is awfully close to quickbuyers, and less than what scrap.tf pays for:

https://i.imgur.com/rzPaEev.png - scrap.tf buys this hat at ~12.5, priced at 18-20. Stormy Bolted Bicorne is 18-21. Scrap.tf buys based on the low-end.

Excluding this sale.

Sale 3:

Bulk for Cyclone Kazotsky

Seller: https://backpack.tf/profiles/76561198173389367#!/compare/1515024000/1515110400

Buyer: https://backpack.tf/profiles/76561198004952793#!/compare/1515024000/1515110400

Sale 4:

Bulk

Seller: https://backpack.tf/profiles/76561198004952793#!/compare/1515628800/1515715200

Buyer: https://backpack.tf/profiles/76561198173389367#!/compare/1515628800/1515715200

Sale 5:

Bulk for Aces Cotton + 2 keys

Seller: https://backpack.tf/profiles/76561198173389367#!/compare/1515715200/1515801600

Buyer: https://backpack.tf/profiles/76561198182795337#!/compare/1515715200/1515801600

Sale 6:

Bulk

Seller: https://backpack.tf/profiles/76561198182795337#!/compare/1516579200/1516665600

Buyer: https://backpack.tf/profiles/76561198104638778#!/compare/1516665600/1516752000

No current sellers.

Going with 19 flat.