Using last month.

Sales 1 & 2:

Sold for $13.33 and $14.50 on marketplace.tf (23 aug, 14 spt)

https://marketplace.tf/items/30843;5;u3001

https://backpack.tf/item/6446109625 - No outpost

http://manic.tf/keyprice/?at=2018-08-23 - $13.33 / $1.9 = 7.02 keys

http://manic.tf/keyprice/?at=2018-09-14 - $14.5 / $1.87 = 7.75 keys

X = 8

X = 7

Sale 3:

Sold for 6 keys

Seller: https://backpack.tf/profiles/76561198388578474#!/compare/1536624000/1536710400

Buyer: https://backpack.tf/profiles/76561198407367604#!/compare/1536710400/1537142400

https://backpack.tf/item/6252906749

The buyer’s name doesn’t appear in the history, but they definitely owned the item if you refer to #5 in the “Other Sales” category.

X = 6

Sale 4:

Quicksold for 5 keys + cheap war paint

Seller: https://backpack.tf/profiles/76561198289781789#!/compare/1536537600/1536796800

Buyer: https://backpack.tf/profiles/76561198388578474#!/compare/1536451200/1536537600

https://backpack.tf/item/6252906749

X = 5

Other Sales:

https://backpack.tf/item/6254481568 (#1)

https://backpack.tf/item/6254356928 (#2)

https://backpack.tf/item/6253019257 (#3)

https://backpack.tf/item/6252906749 (#4)

https://backpack.tf/item/6252906749 (#5)

https://backpack.tf/item/6277797075 - tf2mart

#1

Bulk

https://backpack.tf/profiles/76561198109898906#!/compare/1536278400/1536451200

https://backpack.tf/profiles/76561198364475021#!/compare/1536364800/1536451200

#2

Untraceable

https://backpack.tf/profiles/76561198335791307#!/compare/1534550400/1534636800

https://backpack.tf/profiles/76561198072126409#!/compare/1534550400/1535155200

#3

Untraceable

https://backpack.tf/profiles/76561198208456381#!/compare/1536883200/1537142400

https://backpack.tf/profiles/76561198002757046#!/compare/1537056000/1537142400

#4

Sold for Halloween Fire Degreaser + 1 key

https://backpack.tf/profiles/76561198171095386#!/compare/1536451200/1536537600

https://backpack.tf/profiles/76561198289781789#!/compare/1536451200/1536537600

Seems pretty low.

#5

Bulk for Blizzardy Storm Defiant Spartan

https://backpack.tf/profiles/76561198407367604#!/compare/1536710400/1537142400

https://backpack.tf/profiles/76561198174090699#!/compare/1536883200/1536969600

Sellers:

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

https://backpack.tf/item/6277797075 - ~7.79 keys

https://backpack.tf/item/6252906749 - 8 keys

https://backpack.tf/item/6322349199 - 10 keys

Sales at:

5

6

7

8

My boot scootin' baby is drivin' me crazy

5 quicksold, excluding 5.

Going with 6-8.