Sale 1:

Sold for 18 keys

http://www.tf2outpost.com/trade/28826917 - No B/O

Seller: http://backpack.tf/profiles/76561198002757046#!/compare/1489708800/1489795200

Buyer: http://backpack.tf/profiles/76561198131526809#!/compare/1489708800/1489795200

X = 18

Sale 2:

Sold for Purple Confetti Thirst Blood (Mini at 16 below)

http://www.tf2outpost.com/trade/28813847 - B/O of 20

Seller: http://backpack.tf/profiles/76561198301049636#!/compare/1492387200/1492560000

Buyer: http://backpack.tf/profiles/76561198060968956#!/compare/1492473600/1492560000

X = 16

Sale 3:

Sold for 10 keys?

http://www.tf2outpost.com/trade/28997604 - B/O of 20

Seller: http://backpack.tf/profiles/76561198069754427#!/compare/1494115200/1494201600

Buyer: http://backpack.tf/profiles/76561198014177584#!/compare/1494201600/1494633600

X = 10

Sale 4:

Sold for Aces High Conjurer’s Cowl

Seller: http://backpack.tf/profiles/76561198060968956#!/compare/1492473600/1492560000

Buyer: http://backpack.tf/profiles/76561198054466371#!/compare/1492300800/1492560000

Couldn’t find any sales on the Cowl.

Sale 5:

Sold for Steaming Head Warmer

http://www.tf2outpost.com/trade/28883731 - B/O of 20

Seller: http://backpack.tf/profiles/76561198054466371#!/compare/1492560000/1492646400

Buyer: http://backpack.tf/profiles/76561198083072108#!/compare/1492560000/1492646400

Head Warmer’s price is less than 4 months old, but has a seller at a fair bit less than its current price. Probably better to use this on the Head Warmer instead.

Purple Confetti Thirst Blood Mini:

http://backpack.tf/suggestion/5938f1bbc4404570bd049204

Sellers:

16.3 keys:

http://i.imgur.com/N57KUrk.png - 21 hours, looks to have been lowered, owner has had it for a month

http://backpack.tf/u/76561198304138933

20 keys:

http://i.imgur.com/YrjHyOK.png - 1 months

http://backpack.tf/u/76561198076020691

http://www.tf2outpost.com/trade/28905170

http://i.imgur.com/spB131T.png - 1 months

http://backpack.tf/u/76561198006544512

http://www.tf2outpost.com/trade/28682469

Sales at:

10

16

18

If the sale at 10 is true, it will be pretty low. Excluding 10.

Going with 16-18.