Sales 1, 2, 3, 4 & 5:

Sold for $17, $17.99 (2x), $19.2, and $19.39 on Marketplace.tf

https://marketplace.tf/items/1182;5;u3009

Not gonna bother linking histories

17/1.99 = ~8.54

17.99/1.92 = ~9.37

17.99/1.9 = ~9.47

19.2/1.97 = ~9.746

19.39/1.98 = ~9.79

X = 10

X = 9.5 (3x)

X = 8.5

Sale 6:

Sold with 2 keys + 2.11 ref for Orbiting Planets Glengarry Bonnet (Suggestion at 9)

http://www.tf2outpost.com/trade/29555534 - No B/O

Seller: https://backpack.tf/profiles/76561198106511423#!/compare/1519862400/1519948800

Buyer: https://backpack.tf/profiles/76561198289027466#!/compare/1519689600/1519948800

X = 7

Sale 7:

Sold for ’72 Russian Arms Race

Seller: https://backpack.tf/profiles/76561198257805373#!/compare/1521936000/1522022400

Buyer: https://backpack.tf/profiles/76561198320132670#!/compare/1521936000/1522022400

Can be used on the arms.

Sale 8:

Bulk for pure

Seller: https://backpack.tf/profiles/76561198259342040#!/compare/1521676800/1521763200

Buyer: https://backpack.tf/profiles/76561198808482503#!/compare/1521590400/1521763200

Planets Glengarry:

https://backpack.tf/suggestion/5ac429fd44325a3dba6e6c09

Sellers:

15 keys:

https://i.imgur.com/oZ6hyK1.png

https://backpack.tf/item/6255202827

SCM:

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

$20.13 (~8.15 keys)

$20.42 (~8.27 keys)

$20.79 (~8.42 keys)

$20.83 (~8.43 keys)

$35 (~14.17 keys)

Sales at:

7

8.5

9.5 (3x)

10

Going with 7-10.

2 sellers at 6 in the classifieds:

https://i.imgur.com/fO8tFi2.png

Meanwhile, buyers on the SCM for any effect at 6+ keys:

https://steamcommunity.com/market/listings/440/Unusual%20Taunt%3A%20Yeti%20Punch

This thing's too dumb to be priced rn