Sale 1:

Sold for Chiroptera Venenata Harmburg (80)

No outpost

Seller: https://backpack.tf/profiles/76561198017112652#!/compare/1513641600/1513728000

Buyer: https://backpack.tf/profiles/76561198073002043#!/compare/1513641600/1513728000

X = 80

Sale 2:

Sold for Disco Beat Down Razor Cut (40) + ~12 keys

No outpost

Seller: https://backpack.tf/profiles/76561198152011096#!/compare/1514419200/1514505600

Buyer: https://backpack.tf/profiles/76561198325943865#!/compare/1514419200/1514505600

X = 52

Sale 3:

Sold for Ghastly Ghosts Jr Powdered Practitioner (Mini at 50 below) + 1 key

http://www.tf2outpost.com/trade/29466306 - No visible B/O

Seller: https://backpack.tf/profiles/76561198061376237#!/compare/1513555200/1513641600

Buyer: https://backpack.tf/profiles/76561198017112652#!/compare/1513555200/1513641600

X = 51

Sale 4:

Quicksold for 45 keys

Seller: https://backpack.tf/profiles/76561198073002043#!/compare/1513728000/1513814400

Buyer: https://backpack.tf/profiles/76561198209195433#!/compare/1513728000/1513814400

X = 45

Sale 5:

Sold for Orbiting Fire Cold Killer (Suggestion at 24) + Miami Nights Firewall Helmet (Mini at 13 below) + ~3 keys in items

No outpost

Seller: https://backpack.tf/profiles/76561198209195433#!/compare/1514419200/1514505600

Buyer: https://backpack.tf/profiles/76561198152011096#!/compare/1514419200/1514505600

X = 40

Miami Nights Firewall Mini:

Sold for 13 keys

Seller: https://backpack.tf/profiles/76561197963294617#!/compare/1509235200/1509321600

Buyer: https://backpack.tf/profiles/76561198079356787#!/compare/1508803200/1509321600

X = 13

Orbiting Fire Cold Killer:

https://backpack.tf/suggestion/5a4ee89e44325a607537ccb1

Ghastly Ghosts Jr Practitione Mini:

Sold for 50 keys

Seller: https://backpack.tf/profiles/76561198267189538#!/compare/1513555200/1513641600

Buyer: https://backpack.tf/profiles/76561198017112652#!/compare/1513555200/1513641600

X = 50

Sellers:

~65 keys: (scrap.tf)

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

https://backpack.tf/item/6136125394 - more than a month

Sales at:

40

45

51

52

80

80 is a large outlier. Excluding 80.

45 quicksold, excluding 45 and 40.

Going with 51-52.