Sale 1:

Sold for $45.90 on marketplace.tf

https://marketplace.tf/items/30866;5;u29

https://manic.tf/keyprice/?at=2018-11-02 - $45.9 / $1.78 = 25.79 keys

X = 26

Sale 2:

Sold for Insomnia Wing Mann (Mini at 9.5 below) + Tesla Coil Bandito (Mini at 12.25 below)

Seller: https://backpack.tf/profiles/76561198873310521#!/compare/1544832000/1544918400

Buyer: https://backpack.tf/profiles/76561198799299193#!/compare/1532044800/1544918400

https://backpack.tf/item/6635994092

X = 22

Sale 3:

Sold for 19 keys + 20 ref

Seller: https://backpack.tf/profiles/76561198069751785#!/compare/1544918400/1545004800

Buyer: https://backpack.tf/profiles/76561198126679929#!/compare/1544918400/1545004800

https://backpack.tf/item/6989122292

X = 19

Sale 4:

Sold for 18 keys

Seller: https://backpack.tf/profiles/76561198337734785#!/compare/1544659200/1544745600

Buyer: https://backpack.tf/profiles/76561198090999398#!/compare/1544659200/1544745600

https://backpack.tf/item/6635994092

X = 18

Sale 5:

Sold for 17 keys + 23 ref

Seller: https://backpack.tf/profiles/76561198130439878#!/compare/1544745600/1544832000

Buyer: https://backpack.tf/profiles/76561198326603957#!/compare/1544745600/1544832000

https://backpack.tf/item/6635994092

X = 17

Sale 6:

Sold for 17 keys + 20 ref

Seller: https://backpack.tf/profiles/76561198079417919#!/compare/1544486400/1544572800

Buyer: https://backpack.tf/profiles/76561198069751785#!/compare/1544400000/1544572800

https://backpack.tf/item/6989122292

X = 17

Sale 7:

Sold in less than a day for 16 keys + 20 ref

Seller: https://backpack.tf/profiles/76561198357865695#!/compare/1544400000/1544486400

Buyer: https://backpack.tf/profiles/76561198079417919#!/compare/1544400000/1544486400

https://backpack.tf/item/6989122292

https://i.imgur.com/4eLjLYT.png - bot.tf confirms

X = 16

Sale 8:

Sold to a bot for 15 keys

Seller: https://backpack.tf/profiles/76561198136220673#!/compare/1544400000/1544486400

Buyer: https://backpack.tf/profiles/76561198357865695#!/compare/1544400000/1544486400

https://backpack.tf/item/6989122292

https://i.imgur.com/4eLjLYT.png - bot.tf confirms

X = 15

Sale 9:

Sold for Ominous Night Meet the Medic

Seller: https://backpack.tf/profiles/76561198155927905#!/compare/1541376000/1541462400

Buyer: https://backpack.tf/profiles/76561198254690609#!/compare/1540857600/1541462400

https://backpack.tf/item/6738467229

Better off using on the taunt.

Sale 10:

Sold for Purple Confetti Hot Dogger

Seller: https://backpack.tf/profiles/76561198305394856#!/compare/1545177600/1545350400

Buyer: https://backpack.tf/profiles/76561198021055079#!/compare/1545264000/1545350400

https://backpack.tf/item/6635994092

Should be used on the Hot Dogger

Sale 11:

Sold with 7 keys for Purple Confetti Kiss King

Seller: https://backpack.tf/profiles/76561198090999398#!/compare/1544659200/1544745600

Buyer: https://backpack.tf/profiles/76561198130439878#!/compare/1544659200/1544745600

https://backpack.tf/item/6635994092

Using on the Kiss King.

Sale 12:

Sold with some keys for Terror-Watt Hong Kong Cone

Seller: https://backpack.tf/profiles/76561198326603957#!/compare/1544745600/1544832000

Buyer: https://backpack.tf/profiles/76561198252999692#!/compare/1544745600/1544832000

https://backpack.tf/item/6635994092

Better to use on the Cone.

Sale 13:

Untraceable, appears to be bulk

Seller: https://backpack.tf/profiles/76561198401509004#!/compare/1543276800/1543363200

Buyer: https://backpack.tf/profiles/76561198074625962#!/compare/1543276800/1543363200

https://backpack.tf/item/5973126928

Sale 14:

Untraceable

Seller: https://backpack.tf/profiles/76561198074625962#!/compare/1543795200/1543881600

Buyer: https://backpack.tf/profiles/76561198258168272#!/compare/1543795200/1543881600

https://backpack.tf/item/5973126928

Sale 15:

Untraceable, only 8 keys match

Seller: https://backpack.tf/profiles/76561198258168272#!/compare/1543881600/1544054400

Buyer: https://backpack.tf/profiles/76561198141642028#!/compare/1543881600/1544054400

https://backpack.tf/item/5973126928

Sale 16:

Untraceable

Seller: https://backpack.tf/profiles/76561198252999692#!/compare/1544832000/1544918400

Buyer: https://backpack.tf/profiles/76561198873310521#!/compare/1544832000/1544918400

https://backpack.tf/item/6635994092

Sale 17:

Untraceable

Seller: https://backpack.tf/profiles/76561198254690609#!/compare/1541462400/1541635200

Buyer: https://backpack.tf/profiles/76561198342161127#!/compare/1541376000/1541462400

https://backpack.tf/item/6738467229

Sale 18:

Untraceable

Seller: https://backpack.tf/profiles/76561198136220673#!/compare/1544400000/1544486400

Buyer: https://backpack.tf/profiles/76561198337734785#!/compare/1544400000/1544486400

https://backpack.tf/item/6635994092

Insomnia Wing Mann Mini:

Sale 1:

Sold for 10 keys + 19 ref

Seller: https://backpack.tf/profiles/76561198312583107#!/compare/1542758400/1542844800

Buyer: https://backpack.tf/profiles/76561198074625962#!/compare/1542758400/1542844800

https://backpack.tf/item/5225674460

X = 10.5

Sale 2:

Sold to a bot for 8 keys + 28 ref

Seller: https://backpack.tf/profiles/76561198073884534#!/compare/1543190400/1543276800

Buyer: https://backpack.tf/profiles/76561198308772967#!/compare/1543104000/1543190400

https://backpack.tf/item/6046346364

X = 8.5

Bot.tf supports these sales, as well as this price: https://i.imgur.com/tDplHAC.png

https://bot.tf/stats/item?def=30809&q=5&ef=Starstorm+Insomnia&craft=1&aus=0&ks=0

Taking 9.5.

Tesla Coil Bandito:

Sale 1:

Sold for 13 keys

Seller: https://backpack.tf/profiles/76561198394877897#!/compare/1544400000/1544486400

Buyer: https://backpack.tf/profiles/76561198383050699#!/compare/1543881600/1545436800

https://backpack.tf/item/7209971438

X = 13

Sale 2:

Sold for 11 keys + 22 ref

Seller: https://backpack.tf/profiles/76561198257446982#!/compare/1543104000/1543190400

Buyer: https://backpack.tf/profiles/76561198394877897#!/compare/1543104000/1543190400

https://backpack.tf/item/5253258671

X = 11.5

Sale 3:

Sold for 11 keys + 22 ref

Seller: https://backpack.tf/profiles/76561198139560938#!/compare/1544313600/1544486400

Buyer: https://backpack.tf/profiles/76561198394877897#!/compare/1544400000/1544486400

https://backpack.tf/item/7209971438

X = 11.5

Bot.tf sales support this price: https://i.imgur.com/JyZoYLo.png

https://bot.tf/stats/item?def=30805&q=5&ef=Tesla+Coil&craft=1&aus=0&ks=0

Taking 12.25

Sellers:

https://i.imgur.com/R1PK0P1.png

https://backpack.tf/item/6635994092 - 21 keys

https://backpack.tf/item/6989122292 - ~21.3 keys

https://backpack.tf/item/6622446940 - 23 keys

Sales at:

15

16

17 (2x)

18

19

22

26

https://i.imgur.com/MMLY66X.png - buyers at 15+, excluding 15.

16 quicksold, excluding 16.

Pure sales are common at 17-19. 22 is not a pure sale, and there are two sellers for (slightly) cheaper. Excluding 22, and therefore, 26.

Going with 17-19.