9 month old price!

Sale 1:

Sold for Sunbeams Détective Noir = 55 keys

http://www.tf2outpost.com/trade/28152654

http://backpack.tf/profiles/76561198271848484#!/compare/1463270400/1463356800

http://backpack.tf/profiles/76561198076020691#!/compare/1463184000/1463270400

Sale 2:

Unable to identify sale

[no outpost trade]

http://backpack.tf/profiles/76561197967369676#!/compare/1463788800/1466035200

http://backpack.tf/profiles/76561197967369676#!/compare/1463788800/1466035200

Sale 3: (using to update wet works)

Sold for Searing Plasma Wet Works + 3 keys

http://www.tf2outpost.com/trade/28171870

http://backpack.tf/profiles/76561198271848484#!/compare/1463702400/1463788800

http://backpack.tf/profiles/76561198039834209#!/compare/1463788800/1463875200

Sale 4: (outdated hats but should total to about 50-55 keys)

Sold for Overclocked Le Party Phantom + Miami Nights Belgian Detective = ~50 keys

[no outpost trade]

http://backpack.tf/profiles/76561198126477668#!/compare/1465344000/1465430400

http://backpack.tf/profiles/76561198087962998#!/compare/1465344000/1465430400

Notes:

http://www.tf2outpost.com/trade/28171870 - supposed offer of 50 keys

Conclusion:

Two valid sales at 55 and 50 keys. Taking a final range of 50-55 keys.

Feel free to support/counter my suggestion!