Sale 1:

Sold for 37 keys

Seller: https://backpack.tf/profiles/76561198045607732#!/compare/1550275200/1550361600

Buyer: https://backpack.tf/profiles/76561198287748654#!/compare/1550275200/1550361600

https://backpack.tf/item/1864537531

X = 37

Sale 2:

Sold to a quickbuyer for 32 keys

Seller: https://backpack.tf/profiles/76561198025030539#!/compare/1547942400/1548720000

Buyer: https://backpack.tf/profiles/76561198054758757#!/compare/1548547200/1548720000

https://backpack.tf/item/6801765421

X = 32

Sale 3:

Sold with 5 keys for Eldritch Flame Hellmet (Mini at 25 below) + Orbiting Fire Polar Bear (9.5)

Seller: https://backpack.tf/profiles/76561198038986052#!/compare/1551484800/1551657600

Buyer: https://backpack.tf/profiles/76561198226262240#!/compare/1551571200/1551657600

https://backpack.tf/item/1864537531

X = 30

Sale 4:

Sold in a day for 29 keys

Seller: https://backpack.tf/profiles/76561198002757046#!/compare/1551571200/1551657600

Buyer: https://backpack.tf/profiles/76561198038986052#!/compare/1551484800/1551657600

https://backpack.tf/item/1864537531

X = 29

Other Sales:

https://backpack.tf/item/1864537531 (#1)

#1

Untraceable

https://backpack.tf/profiles/76561198287748654#!/compare/1551312000/1551571200

https://backpack.tf/profiles/76561198002757046#!/compare/1551484800/1551571200

Ancient Eldritch Hellmet Mini:

Sold for 25 keys

Seller: https://backpack.tf/profiles/76561198050518375#!/compare/1548806400/1548892800

Buyer: https://backpack.tf/profiles/76561198034202273#!/compare/1548460800/1548892800

https://backpack.tf/item/7434049772

X = 25

Sellers:

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

https://backpack.tf/item/2796132431 - 36 keys

https://backpack.tf/item/2323489001 - 48 keys

Sales at:

29

30

32

37

Ignoring the fact that the sale at 32 went to a quickbuyer, as buyers are no longer anywhere near that high, and there are sales for cheaper.

29 quicksold, excluding 29.

Going with 30-37.