Rising with duped sales, the only clean version of this hat hasn't been traded in over 3 years.

This is the value for a duped Secret Mullet.

Sale #1:

Sold for Cloud 9 Executioner (50)

http://backpack.tf/profiles/76561198030050182#!/compare/1462406400/1462492800

http://backpack.tf/profiles/76561198138818087#!/compare/1462406400/1462492800

http://www.tf2outpost.com/trade/28049957 Buyout of 45 keys

Sale #2:

Sold with 6 keys for a Stormy 13th Robin (55)

http://www.tf2outpost.com/trade/28145775

http://i.imgur.com/T1R9su6.png

http://backpack.tf/profiles/76561198045214211#!/compare/1463011200/1463097600

http://www.tf2outpost.com/trade/28156774 Mullet was offered here

55 - 6 = 49 keys

Additional Sales:

Sold for Demonflame Tsarboosh (outdated at 32 keys, mini proposes a higher value) + 10 keys

http://backpack.tf/profiles/76561198045214211#!/compare/1462406400/1462579200

Cloud 9 Executioner:

http://backpack.tf/suggestion/573cabd286674728126af5a4

Demonflame Tsarboosh:

Sold with Eldritch Smokey (38) for Knifestorm Pardner's (95)

http://backpack.tf/profiles/76561198022806102#!/compare/1462752000/1462924800

95 - 38 = 57 keys

Not the greatest mini but eh, it's all there is.

http://www.tf2outpost.com/trade/28111517 Had offer of 42 keys for set (other items valued at ~8 keys?) ~34 keys

Knifestorm Pardner's:

http://backpack.tf/profiles/76561198067586587#!/compare/1462320000/1462492800

Sold for 95 keys (it seems)

Conclusion:

Sales are at 45 and 49 keys, the final range can be rounded to 45-50 keys.