2 year old price!

Sale 1:

Sold for 22 keys

http://www.tf2outpost.com/trade/27877269

http://backpack.tf/profiles/76561198096389539/#!/compare/1456041600/1456128000

http://backpack.tf/profiles/76561198073682619/#!/compare/1456041600/1456128000

Sale 2:

Sold for Specialised Australium Knife (~24) + Australium SMG (8) + sweets (~3) = 35 (B/O caps it at 30 keys)

http://www.tf2outpost.com/trade/27890518

http://backpack.tf/profiles/76561198088079103/#!/compare/1457769600/1457856000

http://backpack.tf/profiles/76561198030050182/#!/compare/1457769600/1457856000

Sale 3:

Involved in a bulk deal for Burning Flames Pyro's Boron Beanie

http://www.tf2outpost.com/trade/28020810

http://backpack.tf/profiles/76561198088079103/#!/compare/1460073600/1460160000

Sale 4: (outlier)

Sold with Molten Mallard Doctor's Sack + sweets for Sunbeams Doctor's Sack

[no outpost trade]

http://backpack.tf/profiles/76561198152449073/#!/compare/1455955200/1456041600

http://backpack.tf/profiles/76561198030050182/#!/compare/1455868800/1455955200

Sale 5:

Involved in a bulk deal for Power Surge Blighted Beak

http://www.tf2outpost.com/trade/28068613

http://backpack.tf/profiles/76561198149761601/#!/compare/1460332800/1460505600

Sale 6: (can be used to update the counterfeit billycock)

Sold for Misty Skull Counterfeit Billycock

http://www.tf2outpost.com/trade/27884964

http://backpack.tf/profiles/76561198149761601/#!/compare/1456560000/1456646400

http://backpack.tf/profiles/76561198073682619/#!/compare/1456560000/1456646400

Conclusion:

Two valid sales at 22 and 30 keys. Taking a final range of 22-30 keys.

Feel free to support/counter my suggestion!