Resuggestion!

https://marketplace.tf/items/tf2/31042;5;u7 - 23 / 1.83 = 12.56 ~ 13 Keys

These following sales were found by Shuffle Spy. Thanks!

https://backpack.tf/profiles/76561198197609521#!/compare/1568419200/1568851200 - Unknown amount on SCM

https://backpack.tf/profiles/76561198882886230#!/compare/1567900800/1568246400 - 9 Keys + 22 Refined = ~9.5 Keys

https://backpack.tf/profiles/76561198070684631#!/compare/1491350400/1569888000 - Unknown amount on SCM

https://backpack.tf/profiles/76561198139695263#!/compare/1569456000/1569542400 - Unknown amount on SCM

https://backpack.tf/profiles/76561198308772967#!/compare/1570060800/1570147200 - 8 Keys + 15 Refined (low outlier)

https://backpack.tf/profiles/76561198057511457#!/compare/1566345600/1566432000 - Bulk sale

https://backpack.tf/profiles/76561198259986634#!/compare/1569024000/1569369600 - Sold for 14 Keys

https://backpack.tf/profiles/76561198437335225#!/compare/1567123200/1567296000 - ?

https://backpack.tf/profiles/76561198032515384#!/compare/1567209600/1567296000 - ?

https://backpack.tf/profiles/76561198032515384#!/compare/1567296000/1567382400 - Added 0.5 Keys of Ref for a Terror-Watt Mmmph (9.5 Keys)

https://backpack.tf/profiles/76561198298473489#!/compare/1567900800/1567987200 - Bulk sale

Sales at 9, 9.5, 10, ~12, 13, 14;

Taking 9 - 14 Keys