Sale 1:

Sold for Terror-Watt Hive Minder (Mini at 12 below) + ~5 keys in items

Seller: https://backpack.tf/profiles/76561198061836787#!/compare/1541116800/1541203200

Buyer: https://backpack.tf/profiles/76561198107326934#!/compare/1541030400/1541116800

https://backpack.tf/item/939396722

X = 17

Sale 2:

Sold for Australium Frontier Justice (~9 at the time) + 6 keys + cheap item

Seller: https://backpack.tf/profiles/76561198104340149#!/compare/1544400000/1544486400

Buyer: https://backpack.tf/profiles/76561198396210582#!/compare/1544400000/1544486400

https://backpack.tf/item/1149399784

https://i.imgur.com/9R15UdF.png - bot.tf stats for the frontier justice show purchases at ~9 and sales at ~9.5 in the ~30 day range.

X = 15

Sale 3:

Sold with 3 keys for Subatomic Universal Translator (Mini at 17 below)

Seller: https://backpack.tf/profiles/76561198047019271#!/compare/1541116800/1541203200

Buyer: https://backpack.tf/profiles/76561198133289176#!/compare/1541116800/1541203200

https://backpack.tf/item/5515686450

X = 14

Sale 4:

Sold for 13 keys

Seller: https://backpack.tf/profiles/76561198002757046#!/compare/1545004800/1545091200

Buyer: https://backpack.tf/profiles/76561197999545226#!/compare/1543968000/1545091200

https://backpack.tf/item/5515686450

X = 13

Sale 5:

Untraceable

Seller: https://backpack.tf/profiles/76561197971485686#!/compare/1541116800/1541203200

Buyer: https://backpack.tf/profiles/76561198047019271#!/compare/1541116800/1541203200

https://backpack.tf/item/5515686450

Sale 6:

Untraceable

Seller: https://backpack.tf/profiles/76561198133289176#!/compare/1541203200/1541289600

Buyer: https://backpack.tf/profiles/76561198139385194#!/compare/1520553600/1541203200

https://backpack.tf/item/5515686450

Sale 7:

Untraceable

Seller: https://backpack.tf/profiles/76561198453256831#!/compare/1541203200/1541376000

Buyer: https://backpack.tf/profiles/76561198200222062#!/compare/1541289600/1541376000

https://backpack.tf/item/5515686450

Sale 8:

Untraceable

Seller: https://backpack.tf/profiles/76561198200222062#!/compare/1541289600/1541376000

Buyer: https://backpack.tf/profiles/76561198002757046#!/compare/1541289600/1541376000

https://backpack.tf/item/5515686450

Sale 9:

Untraceable

Seller: https://backpack.tf/profiles/76561198350480132#!/compare/1546041600/1546128000

Buyer: https://backpack.tf/profiles/76561198337734785#!/compare/1545955200/1546041600

https://backpack.tf/item/5515686450

Only 8 keys match.

Sale 10:

Sold for Purple Confetti Steel Shako

Seller: https://backpack.tf/profiles/76561197999545226#!/compare/1545177600/1545264000

Buyer: https://backpack.tf/profiles/76561198350480132#!/compare/1545264000/1546041600

https://backpack.tf/item/5515686450

Using on the Shako.

Sale 11:

Sold for Strange Pro. KS double-spelled Flame Thrower + 3 keys

Seller: https://backpack.tf/profiles/76561198396210582#!/compare/1544486400/1544572800

Buyer: https://backpack.tf/profiles/76561198275735463#!/compare/1544486400/1544572800

https://backpack.tf/item/1149399784

Couldn’t mini this particular flame thrower. I feel that it’ll end up being much higher than sellers though. Excluding this sale.

Sale 12:

Sold for Rockets Yeti Smash + 2 keys

Seller: https://backpack.tf/profiles/76561198149616270#!/compare/1541030400/1541116800

Buyer: https://backpack.tf/profiles/76561197971485686#!/compare/1541030400/1541116800

https://backpack.tf/item/5515686450

Way too low

Sale 13:

Sold for Hellish Inferno Fresh Brewed Victory + ~1 key in items

Seller: https://backpack.tf/profiles/76561198139385194#!/compare/1541203200/1541289600

Buyer: https://backpack.tf/profiles/76561198453256831#!/compare/1541116800/1541203200

https://backpack.tf/item/5515686450

May be better off being used on the taunt.

Sale 14:

Bulk for Acidic Balloonibouncer

Seller: https://backpack.tf/profiles/76561197994783413#!/compare/1540944000/1541030400

Buyer: https://backpack.tf/profiles/76561198149616270#!/compare/1540944000/1541030400

https://backpack.tf/item/5515686450

https://marketplace.tf/items/626;5;u6

https://backpack.tf/item/1149399784 - marketplace sale, but the seller is a scammer fence, excluding. Would most likely fall into the range anyways.

Subatomic Universal Translator Mini:

https://backpack.tf/suggestion/5c28ca3ccf6c752dfc784b60 - refer to my comment

Taking 17.

Terror-Watt Hive Minder Mini:

Sold for 12 keys

https://backpack.tf/profiles/76561198061836787#!/compare/1541203200/1541289600

https://backpack.tf/item/2361310364

Taking 12.

Sellers:

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

https://backpack.tf/item/5515686450 - 13 keys

https://backpack.tf/item/939396722 - 17 keys

https://backpack.tf/item/5437535502 - 19 keys

https://backpack.tf/item/1149399784 - 25 keys

Sales at:

13

14

15

17

Going with 13-17.