Eh screw it i'll just do this real quick.

Taking the "max's head sale" with a grain of salt until someone manages to find it.

Sold for an Australium Flame Thrower(16 Keys)

http://backpack.tf/profiles/76561198006544512#!/compare/1468454400/1468540800

Sold for an Orbiting Fire Gym Rat(~11 Keys)* and ~6 Keys in Sweets

http://backpack.tf/profiles/76561198096565928#!/compare/1463788800/1463875200

*It's outdated, but regardless of what price change this'll have(9 being the lowest), this sale will fit inside the range.

Sold for a Steaming Lucky Shot(15 Keys)

http://backpack.tf/profiles/76561198025076946#!/compare/1466640000/1467072000

http://backpack.tf/profiles/76561198117743929#!/compare/1466812800/1466899200

Sold for a Steaming Rebel Rouser(18 Keys)

http://backpack.tf/profiles/76561198139276623#!/compare/1467849600/1467936000

Sales seem to fit, 15-18 Keys should be fine.

Additional Proof/Counter-Proof/Constructive Criticism/Feedback is always appreciated.