Was doing a suggestion involving this hat, and just my luck, it gets outdated today.

Sold for an Australium Stickybomb Launcher(15 Keys with Overpay at the time) and 2 Keys(17 Keys total)

http://backpack.tf/profiles/76561198109994902?time=1427409316 -> http://backpack.tf/profiles/76561198109994902?time=1427526000

Sold with a Spine-Chilling Skull 2011(2 Keys) for ~19 Keys in Painted items(17 Keys with Overpay)(15 Keys total)

http://backpack.tf/profiles/76561198120667343?time=1431283524 -> http://backpack.tf/profiles/76561198120667343?time=1431327600

Sold for 16 Keys

http://backpack.tf/profiles/76561198094167861?time=1431846000 -> http://backpack.tf/profiles/76561198094167861?time=1431932400

Sales seem to fit, 15-17 Keys should be fine.

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