Sale 1:

Sold with ~5 keys in pure/items for Starstorm Slumber Powdered Practitoner (Suggestion at 33)

No outpost

Seller: https://backpack.tf/profiles/76561198144227819#!/compare/1524009600/1524096000

Buyer: https://backpack.tf/profiles/76561198224552368#!/compare/1524009600/1524096000

X = 28

Sale 2:

Sold for Field Tested Isotope Mannana Peeled Revolver (Mini at 22 below) + ~5 keys in items

http://www.tf2outpost.com/trade/29609399 - B/O of 24

Seller: https://backpack.tf/profiles/76561198376244015#!/compare/1523145600/1523232000

Buyer: https://backpack.tf/profiles/76561198324455724#!/compare/1523145600/1523232000

X = 24 (Capped by B/O)

Sale 3:

Sold for Stormy Storm Buccaneer's Bicorne (Suggestion at 18.5) through auction

Seller: https://backpack.tf/profiles/76561198336156500#!/compare/1523664000/1523836800

Buyer: https://backpack.tf/profiles/76561198211889876#!/compare/1523404800/1523836800

X = 19

Sale 4:

Sold with 2 keys for Strange Stormy Storm Blast Defense (Suggestion at 16.5)

http://www.tf2outpost.com/trade/29619035 - B/O of 23

Seller: https://backpack.tf/profiles/76561198324455724#!/compare/1523923200/1524009600

Buyer: https://backpack.tf/profiles/76561198144227819#!/compare/1523923200/1524009600

X = 15

Sale 5:

Bulk for Hot Scattergun

Seller: https://backpack.tf/profiles/76561198333597703#!/compare/1523664000/1523836800

Buyer: https://backpack.tf/profiles/76561198336156500#!/compare/1523491200/1523664000

Isotope Mannana Revolver Mini:

Sale 1:

Sold with 2 keys for Nether Trail Smokey Sombrero (Suggestion at 24)

Seller: https://backpack.tf/profiles/76561198376244015#!/compare/1523404800/1523491200

Buyer: https://backpack.tf/profiles/76561198041207018#!/compare/1523491200/1523577600

X = 22

Sale 2:

Sold with ~7 keys in items for Neutron Star Noble Nickel

Seller: https://backpack.tf/profiles/76561198041207018#!/compare/1523664000/1524096000

Buyer: https://backpack.tf/profiles/76561198053767371#!/compare/1523664000/1523750400

Should not be used here.

Nether Trail Sombrero:

https://backpack.tf/suggestion/5ae05668cf6c753c79536983

Slumber Practitioner:

https://backpack.tf/suggestion/5ae059aa44325a2cb05107fb

Strange Stormy Blast Defense:

https://backpack.tf/suggestion/5ae049ddcf6c7530c074cf11

Stormy Bicorne:

https://backpack.tf/suggestion/5ae04db144325a28152ca03d

Sellers:

23 keys:

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

https://backpack.tf/item/5186184240

https://i.imgur.com/E5dWJ2X.png

https://backpack.tf/item/6678422752

40 keys:

http://www.tf2outpost.com/trade/29517103

52 keys:

https://i.imgur.com/mCcP9Gz.png

https://backpack.tf/item/6410276971

SCM: (Taking keys as $2.47)

https://i.imgur.com/8jwsSM3.png (Only the first 2 are important here)

$42.84 (~17.3 keys)

$57.41 (~23.2 keys)

Sellers at 23 have been there for a fair amount of time, and Sale 1 would most likely be lower if we knew the B/O. Excluding 24 and 29.

Going with 15-19.