Sale 1:

Sold with 12 keys + ~3 keys in items for Galactic Gateway Tank Top (51)

Seller: https://backpack.tf/profiles/76561198192411802#!/compare/1550361600/1550448000

Buyer: https://backpack.tf/profiles/76561198130990555#!/compare/1550361600/1550448000

https://backpack.tf/item/3482930938

X = 36

Sale 2:

Sold with 2 keys + metal for Planets Brotherhood of Arms (Suggestion at 27.5)

Seller: https://backpack.tf/profiles/76561198060801935#!/compare/1547078400/1547424000

Buyer: https://backpack.tf/profiles/76561198089739855#!/compare/1547251200/1547424000

X = 26

Sale 3:

Sold for 23 keys

Seller: https://backpack.tf/profiles/76561197970562873#!/compare/1550275200/1550448000

Buyer: https://backpack.tf/profiles/76561198148836514#!/compare/1550361600/1550448000

https://backpack.tf/item/6306109566

X = 23

Marketplace Sales:

https://marketplace.tf/items/30123;5;u7

https://manic.tf/keyprice/?at=2018-11-30 - $35.56 / $1.72 = 20.67 keys

X = 21

Other Sales:

https://backpack.tf/item/6306109566 (#1 & #2)

https://backpack.tf/item/3482930938 (#3-5)

https://backpack.tf/item/7338264878 - scammers

#1

Untraceable

https://backpack.tf/profiles/76561198076587490#!/compare/1550707200/1550793600

https://backpack.tf/profiles/76561198105071091#!/compare/1550620800/1550707200

#2

Sold with 5 keys for Smoking Brotherhood of Arms

https://backpack.tf/profiles/76561198148836514#!/compare/1550534400/1550620800

https://backpack.tf/profiles/76561198076587490#!/compare/1550448000/1550620800

Gonna be waaaaaay too high, excluding.

#3

Bulk for Logo KE

https://backpack.tf/profiles/76561198074275586#!/compare/1546992000/1547078400

https://backpack.tf/profiles/76561198060801935#!/compare/1546819200/1547078400

#4

Sold for Vivid Caribou Companion + Uncraftable Pink Paint

https://backpack.tf/profiles/76561198089739855#!/compare/1548720000/1550275200

https://backpack.tf/profiles/76561198273253162#!/compare/1548720000/1548806400

Better off being used on the Caribou.

#5

Sold for Scorching Head Hedge

https://backpack.tf/profiles/76561198273253162#!/compare/1550275200/1550361600

https://backpack.tf/profiles/76561198192411802#!/compare/1550188800/1550275200

This’ll also be pretty high.

Planets Brotherhood of Arms:

https://backpack.tf/suggestion/5c67d1dbcf6c757f810a972c

Sellers:

https://i.imgur.com/I4wP9De.png

https://backpack.tf/item/6306109566 - 39 keys

https://backpack.tf/item/3482930938 - 40 keys

https://backpack.tf/item/5483959461 - 42 keys

Sales at:

21

23

26

36

https://i.imgur.com/kCwxfik.png - buyers at 23, excluding 21 and 23.

Going with 26-36.