Sale 1:

Sold for 45 keys

Seller: https://backpack.tf/profiles/76561198314211872#!/compare/1549497600/1549584000

Buyer: https://backpack.tf/profiles/76561198163266519#!/compare/1549411200/1549584000

https://backpack.tf/item/270960534

https://i.imgur.com/mm5KB8m.png - bot.tf confirms

X = 45

Sale 2:

Sold for 45 keys?

Seller: https://backpack.tf/profiles/76561198074924284#!/compare/1544745600/1544832000

Buyer: https://backpack.tf/profiles/76561198072140772#!/compare/1544400000/1544832000

https://backpack.tf/item/206131504

Hat was modified (painted), and the keys were bought on marketplace before being scanned in the buyers backpack most likely, so histories and ID’s aren’t gonna match, though I don’t doubt that it sold for 45 keys here. Even if it didn’t, it won’t affect the range here.

X = 45

Sale 3:

Sold for 40 keys + ~2 keys in painted items and metal

Seller: https://backpack.tf/profiles/76561198160856661#!/compare/1548633600/1548720000

Buyer: https://backpack.tf/profiles/76561198150610648#!/compare/1548633600/1548720000

https://backpack.tf/item/678538172

X = 42

Sale 4:

Sold for 40 keys

Seller: https://backpack.tf/profiles/76561198305494036#!/compare/1547078400/1547164800

Buyer: https://backpack.tf/profiles/76561198104168501#!/compare/1547078400/1547164800

https://backpack.tf/item/206131504

https://i.imgur.com/mm5KB8m.png - bot.tf confirms

X = 40

Sale 5:

Sold for 39 keys

Seller: https://backpack.tf/profiles/76561198096856475#!/compare/1547251200/1547337600

Buyer: https://backpack.tf/profiles/76561198257628196#!/compare/1547164800/1547337600

https://backpack.tf/item/270960534

X = 39

Sale 6:

Sold for 36 keys + 7 ref

Seller: https://backpack.tf/profiles/76561198257628196#!/compare/1549152000/1549411200

Buyer: https://backpack.tf/profiles/76561198314211872#!/compare/1549324800/1549411200

https://backpack.tf/item/270960534

https://i.imgur.com/mm5KB8m.png - bot.tf confirms

X = 36

Marketplace Sales:

https://marketplace.tf/items/147;5;u14

https://manic.tf/keyprice/?at=2018-12-25 - $75 / $1.8 = 41.67 keys

X = 42

Other Sales:

https://backpack.tf/item/678538172 (#1)

https://backpack.tf/item/270960534 (#2)

https://backpack.tf/item/206131504 (#3-6)

#1

Bulk for Roboactive Lucky Shot

https://backpack.tf/profiles/76561198117522318#!/compare/1546214400/1546300800

https://backpack.tf/profiles/76561198160856661#!/compare/1546214400/1546300800

#2

Bulk for Purple Confetti Blighted Beak

https://backpack.tf/profiles/76561198045968907#!/compare/1546646400/1546992000

https://backpack.tf/profiles/76561198096856475#!/compare/1546905600/1546992000

Using on the Beak.

#3

Bulk for Burning Le Party Phantom

https://backpack.tf/profiles/76561198072140772#!/compare/1545868800/1545955200

https://backpack.tf/profiles/76561198071983249#!/compare/1545782400/1545868800

#4

Bulk

https://backpack.tf/profiles/76561198071983249#!/compare/1546128000/1546214400

https://backpack.tf/profiles/76561198160856661#!/compare/1546128000/1546214400

https://i.imgur.com/mm5KB8m.png - labelled as a 35 key + 35 ref purchase

#5

Untraceable

https://backpack.tf/profiles/76561198104168501#!/compare/1550793600/1550966400

https://backpack.tf/profiles/76561198447257724#!/compare/1550880000/1550966400

#6

Untraceable

https://backpack.tf/profiles/76561198104168501#!/compare/1550793600/1550966400

https://backpack.tf/profiles/76561198447257724#!/compare/1550880000/1550966400

Sellers:

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

https://backpack.tf/item/206131504 - 50 keys

Sales at:

36

39

40

42 (2x)

45 (2x)

36 went to a quickbuyer, and there are currently several buyers at 36+. Excluding 36.

Going with 39-45.