Using last month.

Sale 1:

Sold for Logo Sober Stuntman (Suggestion at 9.75)

Seller: https://backpack.tf/profiles/76561198380114520#!/compare/1531958400/1532131200

Buyer: https://backpack.tf/profiles/76561198367264041#!/compare/1531958400/1532131200

X = 10

Sale 2:

Sold for 9 keys (ID’s match)

Seller: https://backpack.tf/profiles/76561198081172172#!/compare/1531353600/1531440000

Buyer: https://backpack.tf/profiles/76561198240433090#!/compare/1531440000/1531958400

X = 9

Sale 3:

Sold for 9 keys (ID’s match)

Seller: https://backpack.tf/profiles/76561198024867201#!/compare/1530835200/1530921600

Buyer: https://backpack.tf/profiles/76561197980575764#!/compare/1530748800/1530921600

X = 9

Sale 4:

Sold for Mega Strike Luxury Lounge (Suggestion at 9)

No outpost

Seller: https://backpack.tf/profiles/76561198256956241#!/compare/1531526400/1531612800

Buyer: https://backpack.tf/profiles/76561198296316015#!/compare/1531526400/1531612800

X = 9

Sale 5:

Sold for Bubbling Prancer’s Pride (Suggestion at 8)

No outpost

Seller: https://backpack.tf/profiles/76561198204215085#!/compare/1530748800/1530921600

Buyer: https://backpack.tf/profiles/76561198281956556#!/compare/1530835200/1530921600

X = 8

Sale 6:

Sold to a quickbuyer for 7 keys + 10 ref

Seller: https://backpack.tf/profiles/76561198367264041#!/compare/1531958400/1532131200

Buyer: https://backpack.tf/profiles/76561198203307876#!/compare/1532044800/1532131200

X = 7.5

Sale 7:

Sold to a bot for 6 keys + 8 ref

Seller: https://backpack.tf/profiles/76561198281956556#!/compare/1531094400/1531180800

Buyer: https://backpack.tf/profiles/76561198335791307#!/compare/1531008000/1531180800

Bot.tf confirms: https://i.imgur.com/1N0f6uR.png

X = 6

Sales 8-10:

Sold for $29.99 (2x) and $28.99 on marketplace.tf

https://marketplace.tf/items/30920;5;u3005

All these sales are significantly higher than the other sales, as well as the current sellers. Excluding them.

Sale 11:

Bulk for Burning Fukaa

Seller: https://backpack.tf/profiles/76561197980575764#!/compare/1531180800/1531267200

Buyer: https://backpack.tf/profiles/76561198342161127#!/compare/1531180800/1531267200

Sale 12:

Bulk for Logo Belt

Seller: https://backpack.tf/profiles/76561198044607677#!/compare/1531612800/1531699200

Buyer: https://backpack.tf/profiles/76561198380114520#!/compare/1531526400/1531612800

Bubbling Prancer’s Pride:

https://backpack.tf/suggestion/5b5931de44325a216712c061

Logo Stuntman:

https://backpack.tf/suggestion/5b593aad44325a216f71096f

Mega Strike Luxury:

https://backpack.tf/suggestion/5b593fd3cf6c7511c411f4cd

Sellers:

10 keys:

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

https://backpack.tf/item/6496521222

~11.5 keys:

https://i.imgur.com/lf7ZJeP.png

https://backpack.tf/item/6459008900

https://backpack.tf/item/6558514699

Sales at:

6

7.5

8

9 (3x)

10

6 is lower than current buyers, excluding.

7.5 is not a common trading point, excluding.

Going with 8-10.

Update:

No new sales, but the Mega Strike Luxury Lounge (Sale 4) is now being updated to 8 keys:

https://backpack.tf/suggestion/5b65145a44325a0e5c68ebaa

Still fits in the range.