Sale 1:

Sold for Spec. KS Aussie Scattergun (~24 at the time)

No outpost

Seller: https://backpack.tf/profiles/76561198129307198#!/compare/1513728000/1513814400

Buyer: https://backpack.tf/profiles/76561198257674916#!/compare/1513296000/1513814400

X = 24

Sale 2:

Sold for 18 keys in ~1 day

Seller: https://backpack.tf/profiles/76561198209195433#!/compare/1511740800/1511827200

Buyer: https://backpack.tf/profiles/76561198364127001#!/compare/1511740800/1511827200

X = 18

Sale 3:

Sold with cheap skin for Kill-a-Watt Prince Tavish’s Crown (Suggestion at 18)

http://www.tf2outpost.com/trade/29491526 - couldn’t find the B/O in this mess.

Seller: https://backpack.tf/profiles/76561198348845919#!/compare/1514246400/1514505600

Buyer: https://backpack.tf/profiles/76561198055553140#!/compare/1514419200/1514505600

X = 18

Sale 4:

Sold for 16 keys

Seller: https://backpack.tf/profiles/76561198164651434#!/compare/1514851200/1514937600

Buyer: https://backpack.tf/profiles/76561198025083656#!/compare/1514851200/1514937600

X = 16

Sale 5:

Sold for 14 keys

Seller: https://backpack.tf/profiles/76561198344933095#!/compare/1514764800/1514851200

Buyer: https://backpack.tf/profiles/76561198147262884#!/compare/1514851200/1515110400

X = 14

Sale 6:

Sold for 12 keys

Seller: https://backpack.tf/profiles/76561198257674916#!/compare/1514246400/1514332800

Buyer: https://backpack.tf/profiles/76561198042132655#!/compare/1514246400/1514332800

X = 12

Sale 7:

Sold for 11 keys to a quickbuyer

Seller: https://backpack.tf/profiles/76561198348999481#!/compare/1512864000/1512950400

Buyer: https://backpack.tf/profiles/76561198267189538#!/compare/1512864000/1512950400

X = 11

Sale 8:

Bulk for Grail Bronco

Seller: https://backpack.tf/profiles/76561198364127001#!/compare/1513209600/1513296000

Buyer: https://backpack.tf/profiles/76561198286234945#!/compare/1513209600/1513296000

Sale 9:

Sold for Vivid Plasma Elf Esteem

Seller: https://backpack.tf/profiles/76561198368095838#!/compare/1514073600/1514160000

Buyer: https://backpack.tf/profiles/76561198348845919#!/compare/1514073600/1514160000

Seems pretty low, especially with the seller at 11 on the Elf. Excluding.

Sale 10:

Bulk for Strange Burning Noble

Seller: https://backpack.tf/profiles/76561198125791160#!/compare/1511222400/1511308800

Buyer: https://backpack.tf/profiles/76561198326172306#!/compare/1511222400/1511308800

Sale 11:

Bulk for Spellbound Ballcap

Seller: https://backpack.tf/profiles/76561198326172306#!/compare/1512345600/1512518400

Buyer: https://backpack.tf/profiles/76561198129307198#!/compare/1512432000/1512518400

Kill-a-Watt Prince Tavish’s Crown:

https://backpack.tf/suggestion/5a509517cf6c754da3281d9f

Sellers:

16 keys:

https://i.imgur.com/Cp6wvRl.png - 1 day

24 keys:

https://i.imgur.com/5OXthmV.png - 18 days

40 keys:

https://i.imgur.com/c7KFQO3.png - young

Sales at:

11

12

14

16

18 (2x)

24

11 went to a quickbuyer, excluding.

excluding 24 due to the seller at 24 being kinda old, and because 24 looks like an outlier.

12 looks like a bit of an outlier, and is pretty close to the quickbuy at 11.

Cheers Lemons for advice on the range

Going with 14-18.