Using last month.

Sales 1-4:

Sold for $29.75, $25.49, $23.99, & $20.19 on marketplace.tf

https://marketplace.tf/items/477;5;u3006

http://manic.tf/keyprice/?at=2018-10-01 - $29.75 / $1.83 = 16.26 keys

http://manic.tf/keyprice/?at=2018-09-30 - $25.49 / $1.84 = 13.85 keys

http://manic.tf/keyprice/?at=2018-09-29 - $23.99 / $1.84 = 13.04 keys

http://manic.tf/keyprice/?at=2018-09-22 - $20.19 / $1.84 = 10.97 keys

X = 16

X = 14

X = 13

X = 11

Other Sales:

https://backpack.tf/item/6820527626 (#1-3)

https://backpack.tf/item/2089330432 (#4)

https://backpack.tf/item/6724210776 - marketplace

https://backpack.tf/item/6481201404 - marketplace

https://backpack.tf/item/5418950753 - marketplace

https://backpack.tf/item/5380609097 - scrap

https://backpack.tf/item/2490870938 - probably traded between friends

#1

https://backpack.tf/profiles/76561198334598690#!/compare/1538524800/1538611200

https://backpack.tf/profiles/76561198826682248#!/compare/1538524800/1538611200

labelled as 13, but only 11 appear here, some keys were most likely spent on the day the item sold - https://i.imgur.com/bIV0IJK.png

#2

Bulk for pure

https://backpack.tf/profiles/76561198826682248#!/compare/1538611200/1538870400

https://backpack.tf/profiles/76561198311498888#!/compare/1538784000/1538870400

#3

Untraceable

https://backpack.tf/profiles/76561198327163757#!/compare/1537228800/1538265600

https://backpack.tf/profiles/76561198334598690#!/compare/1538179200/1538265600

https://i.imgur.com/bIV0IJK.png - labelled as 8 keys and 14.66 ref

#4

Bulk for Duped Spellbound Whoopee Cap?

https://backpack.tf/profiles/76561198062711407#!/compare/1538352000/1538438400

https://backpack.tf/profiles/76561198065132511#!/compare/1538438400/1538524800

Sellers:

https://i.imgur.com/rh0kJoO.png

https://backpack.tf/item/1829387458 - 12 keys

https://backpack.tf/item/6937127296 - 13 keys

https://backpack.tf/item/4848773819 - 13 keys

https://backpack.tf/item/3294817138 - 140 keys

Sales at:

11

13

14

16

Month-unsold at 13, going to exclude anything higher.

Going with 11-13.

Bulk for duped Cloudy Moon Grenadier's Softcap

https://backpack.tf/profiles/76561198242214772#!/compare/1539907200/1540166400

https://backpack.tf/profiles/76561197964171516#!/compare/1539820800/1539907200

sold to a bot for 8 keys and 1 scrap

https://backpack.tf/profiles/76561198091280339#!/compare/1539302400/1540857600

https://backpack.tf/profiles/76561198305676157#!/compare/1540771200/1540857600

https://i.imgur.com/SpPS5T6.png

being re-sold for 11 keys, also one of the 13 key sellers have dropped to 12

https://i.imgur.com/dfMl04b.png

not sure if i should keep 13.