Making a range. Also outdated.

http://www.tf2outpost.com/trade/25803048

Selling for 23 keys

http://www.tf2outpost.com/trade/24884718

Selling for 23 keys

http://backpack.tf/stats/Unusual/Burning%20Bandana/Tradable/Craftable/61

Includes the 2 above, the one at 25 is "willing to negotiate x Cheapest on bp.tf," suggesting that he would likely accept 23 keys.

http://puu.sh/htqUX/6f4c2d4e98.jpg

Was selling for 24, offered his Bandana + 3 keys on a Disco Beat Down Stormin' Norman according to this conversation: http://puu.sh/htqUX/6f4c2d4e98.jpg and http://i.imgur.com/NseAn2J.png

Mini on the Normal=================================================================================================

http://www.tf2outpost.com/trade/25794825

Selling for 20!

http://www.tf2outpost.com/trade/23680826

Selling for 24

http://www.tf2outpost.com/trade/25075134

Was selling for 20, backpack.tf does not show what he sold it for. Presumably real world money.

All other sales are either outdated or for CS:GO items, placing the item at around 24 (with overpay). 24 - 3 = 21. The Bandana here would be 21.

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http://www.tf2outpost.com/trade/24620971

Sold for 18 keys according to backpack.tf history: http://backpack.tf/profiles/76561197995427553?time=1421136000 and http://backpack.tf/profiles/76561197995427553?time=1421222400. Notice the keys in the January 13 backpack. I checked through all the histories of the 22 keys in the January 14 backpack to find that 4 of them were from another source (not from EGC | Λρρℓℰ Pawnshop, the current owner at the time of this suggestion). Don't believe me?

http://backpack.tf/item/2862661168

http://backpack.tf/item/2783617637

http://backpack.tf/item/3346505795

http://backpack.tf/item/2952621596

All from xXSubzeroXx

Sale at 18 and sale at 21 with B/O's at 23.