Sales 1, 2, 3, & 4:

Sold for $17.99, $17.98, $15 and $14.88 on Marketplace.tf

https://marketplace.tf/items/30843;5;u3008

https://backpack.tf/item/6478769318 - $17.98

https://backpack.tf/item/6488955115 - $17.99

Can't find the other ones

17.99/1.99 = ~9.04

17.98/1.98 = ~9.08

15/1.95 = ~7.69

14.88/1.94 = ~7.67

http://www.tf2outpost.com/trade/29539920 - B/O of 9 on the $17.99 sale

http://www.tf2outpost.com/trade/29583725 - B/O of 6 on the $17.98 sale, confirmed by ya boi https://i.imgur.com/cMWhkIt.png

X = 9

X = 6 (Capped by B/O)

X = 7.5 (2x)

Sale 5:

Bot.tf sale at 6 keys

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

https://backpack.tf/profiles/76561198086076383#!/compare/1521936000/1522022400 - Might be this trade, not sure. Went to a sfuminator bot, don't know if there was another owner prior to that.

https://backpack.tf/item/6290036558

X = 6

Sale 6:

Sold for 5 keys

Seller: https://backpack.tf/profiles/76561198005273439#!/compare/1521244800/1521331200

Buyer: https://backpack.tf/profiles/76561198195171558#!/compare/1521244800/1521331200

X = 5

Sale 7:

Bulk for Green Energy Festive Tree

Seller: https://backpack.tf/profiles/76561198082210257#!/compare/1521504000/1521590400

Buyer: https://backpack.tf/profiles/76561198162282453#!/compare/1521590400/1521676800

Sellers:

7 keys:

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

https://backpack.tf/item/6285405526

https://backpack.tf/item/6256607714

15 keys:

https://i.imgur.com/8auIKvg.png

https://backpack.tf/item/6252895774

19 keys:

https://i.imgur.com/f6m4x8A.png

https://backpack.tf/item/6272251275

https://backpack.tf/item/6281021231

https://backpack.tf/item/6252906972

Sales at:

5

6 (2x)

7.5 (2x)

9

Quickbuyer at 5 keys:

https://i.imgur.com/rD9rpRB.png

Excluding 5.

7 is looking like an outlier, given the seller at 7 that has two listed. Excluding 9.

Going with 6-7.5.