Using last month.

Sales 1 & 2

Sold for $25 and $9.06 on marketplace.tf

$9.06 is gonna be way too low.

https://marketplace.tf/items/1168;5;u3001

http://manic.tf/keyprice/?at=2018-08-27 - $25 / $1.89 = 13.23 keys

Couldn’t find item histories.

X = 13

Sale 3:

Sold for 12 keys + ~1 key in metal

Seller: https://backpack.tf/profiles/76561198024867201#!/compare/1535155200/1535241600

Buyer: https://backpack.tf/profiles/76561198149688091#!/compare/1535155200/1535241600

https://backpack.tf/item/4961923865

X = 13

Sale 4:

Sold for 12 keys

Seller: https://backpack.tf/profiles/76561198334598690#!/compare/1536969600/1537056000

Buyer: https://backpack.tf/profiles/76561198085852627#!/compare/1536969600/1537056000

https://backpack.tf/item/7108746959

https://i.imgur.com/3NEDjIJ.png

We only see 11 keys here, but I doubt bot.tf is wrong in this case.

X = 12

Sale 5:

Sold for 9 keys + cheap cosmetic

Seller: https://backpack.tf/profiles/76561198051616613#!/compare/1536710400/1536796800

Buyer: https://backpack.tf/profiles/76561198082708308#!/compare/1533513600/1537228800

https://backpack.tf/item/5400687375

X = 9

Other Sales:

https://backpack.tf/item/7108746959 (#1)

https://backpack.tf/item/5400687375 (#2)

https://backpack.tf/item/5095761991 (#3)

https://backpack.tf/item/5007461499 (#4)

https://backpack.tf/item/4968247134 (#5)

https://backpack.tf/item/6747053360 - swap bot

https://backpack.tf/item/5354887472 - tradeit/swap bots

https://backpack.tf/item/4954432166 - marketplace stuff

#1

Untraceable

https://backpack.tf/profiles/76561198043997760#!/compare/1535673600/1535760000

https://backpack.tf/profiles/76561198334598690#!/compare/1535673600/1535760000

https://i.imgur.com/3NEDjIJ.png - labelled as 7 keys + 12 ref

#2

Untraceable/likely bulk

https://backpack.tf/profiles/76561198131755309 - inventory service unavailable at the time

https://backpack.tf/profiles/76561198051616613#!/compare/1536451200/1536710400

#3

Untraceable

https://backpack.tf/profiles/76561198081706519#!/compare/1535932800/1536364800

https://backpack.tf/profiles/76561198097271466#!/compare/1536278400/1536364800

#4

Untraceable

https://backpack.tf/profiles/76561198119163692#!/compare/1534982400/1535068800

https://backpack.tf/profiles/76561198116779194#!/compare/1534809600/1535328000

#5

Probably gambled

https://backpack.tf/profiles/76561198110011480#!/compare/1537401600/1537488000

https://backpack.tf/profiles/76561198197481041#!/compare/1537401600/1537488000

Sellers:

https://i.imgur.com/tiECF5k.png

https://backpack.tf/item/5095761991 - 13 keys

https://backpack.tf/item/4952898500 - 45 keys

https://backpack.tf/item/6780885154 - 50.56 keys

And another on marketplace.tf for ~11 keys

https://marketplace.tf/items/1168;5;u3001

Sales at:

9

12

13 (2x)

Going with 9-13.