Using last month

Sales 1 & 2:

Sold for $14.30 and $13.89 on Marketplace.tf

https://marketplace.tf/items/1120;5;u3010

14.3/1.97 = ~7.26

13.89/1.97 = ~7.05

X = 7.5

X = 7

Sale 3:

Sold for 6 keys + 20 ref

Seller: https://backpack.tf/profiles/76561198344933095#!/compare/1524787200/1524873600

Buyer: https://backpack.tf/profiles/76561198164041055#!/compare/1524787200/1524873600

Bot.tf stats: https://i.imgur.com/6xw1SG2.png

X = 6.5

Sale 4:

Sold for 6 keys

Seller: https://backpack.tf/profiles/76561198129386527#!/compare/1523664000/1523750400

Buyer: https://backpack.tf/profiles/76561198093511899#!/compare/1521676800/1524182400

X = 6

Sale 5:

Bulk for Cloudy Moon Attendant

Seller: https://backpack.tf/profiles/76561198105071091#!/compare/1523145600/1523232000

Buyer: https://backpack.tf/profiles/76561198066511271#!/compare/1523232000/1523318400

Sale 6:

Bulk for Stormy YWN and other things

Seller: https://backpack.tf/profiles/76561198796493509#!/compare/1522368000/1522540800

Buyer: https://backpack.tf/profiles/76561198362185176#!/compare/1522454400/1522540800

Sale 7:

???

Seller: https://backpack.tf/profiles/76561198254375254#!/compare/1523059200/1523145600

Buyer: https://backpack.tf/profiles/76561198107859924#!/compare/1522972800/1523145600

Sellers:

9 keys:

https://i.imgur.com/lVYI72z.png

https://backpack.tf/item/5947896344

20 keys:

https://i.imgur.com/quhY2FQ.png

https://backpack.tf/item/2918352807

22 keys:

https://i.imgur.com/6LI8JMp.png

https://backpack.tf/item/5745586731

Offers:

http://www.tf2outpost.com/trade/29627572

Sales at:

6

6.5

7

7.5

Going with 6-7.5.