Sales supporting the price:

Sale 1:

Sold for Duped Phosphorus Geisha Boy

Cannot find Outpost link

Seller: http://backpack.tf/profiles/76561198125791160/#!/compare/1456214400/1456300800

Buyer: http://backpack.tf/profiles/76561198072845816/#!/compare/1456214400/1456300800

Geisha Boy Mini:

Sold for:

Disco Beat Down Screamin' Eagle (35)

Strange Spec. KS Sniper Rifle (1.5)

Strange Anger w/ Parts (2)

Strange Killstreak Disciplinary Action (2.5)

http://www.tf2outpost.com/trade/27887493 - No B/O

Seller: http://backpack.tf/profiles/76561198125791160/#!/compare/1456387200/1456473600

Buyer: http://backpack.tf/profiles/76561198128344327/#!/compare/1456473600/1456560000

X = 35 + 2.5 + 2 + 1.5

X = 41

Appears to be the only sale on this item.

Sale 2:

Sold for Lantern Dead Cone + Dead Presidents Big Elfin Deal

http://www.tf2outpost.com/trade/27837691 - B/O deleted, probably

Seller: http://backpack.tf/profiles/76561198067055238/#!/compare/1455436800/1455523200

Buyer: http://backpack.tf/profiles/76561198136517766/#!/compare/1455436800/1455523200

Proof of the Elfin Deal: http://www.tf2outpost.com/item/440,4285507384 (Noob --> Hatman)

X = 19.5 + 15

X = 34.5

Rounding to 35

Sale 3:

Quicksold for 26? keys

http://www.tf2outpost.com/trade/27908745

Seller: http://backpack.tf/profiles/76561198261183816/#!/compare/1456732800/1456819200

Buyer: http://backpack.tf/profiles/76561198002757046/#!/compare/1456732800/1456819200

Sold in about 1 day, excluding from range

Additional Sales:

Sale 4:

Bulk for Burning Front Runner

Seller: http://backpack.tf/profiles/76561198124846866/#!/compare/1454659200/1454745600

Buyer: http://backpack.tf/profiles/76561198135763017/#!/compare/1454659200/1454745600

Sale 5:

Bulk for something

Seller: http://backpack.tf/profiles/76561198135763017/#!/compare/1455091200/1455177600

Buyer: http://backpack.tf/profiles/76561198125791160/#!/compare/1455177600/1455264000

Sale 6:

Bulk for Searing Cold Killer

Seller: http://backpack.tf/profiles/76561198128604013/#!/compare/1455091200/1455264000

Buyer: http://backpack.tf/profiles/76561198067055238/#!/compare/1455177600/1455264000

Sale 7:

Bulk for Purple Energy Festive Tree

No outpost link available

Seller: http://backpack.tf/profiles/76561198214598141/#!/compare/1456646400/1456732800

Buyer: http://backpack.tf/profiles/76561198261183816/#!/compare/1456646400/1456732800

Sale 8:

Sold for Factory New Shot to Hell Pistol?

Seller: http://backpack.tf/profiles/76561198072845816/#!/compare/1456214400/1456300800

Buyer: http://backpack.tf/profiles/76561198066953778/#!/compare/1455004800/1456732800

Not even going to touch this sale. The pistol could be anywhere near 100 keys probably.

Sale 9:

Sold with Hot Pro. KS Woodsy Widowmaker Machine Gun (Field Tested) for Orbiting Fire Bonk Boy

No outpost link available

Seller: http://backpack.tf/profiles/76561198136517766/#!/compare/1456560000/1456646400

Buyer: http://backpack.tf/profiles/76561198214598141/#!/compare/1456560000/1456646400

Bonk Boy: http://backpack.tf/item/1503603420

This is most likely an outlier, as it would bring the Bandana to around ~15-20 keys.

Sellers:

30 keys:

http://puu.sh/nsR5l/e8b6fc276a.png - 1 day, kinda young, so excluding from range, unless told otherwise.

36 keys:

http://puu.sh/nsR2I/af2afa41e8.png - 6 days, unbumped

Three sales at:

26 (quicksold)

35

41

Going with 35-41