The invasion update came out exactly a year and a half ago. Feels like it was just a few months ago, though. At least, to me.

Sold for 20 Keys

http://backpack.tf/profiles/76561198113083770#!/compare/1488844800/1488931200

Sold for 13.5 Keys and an Australium Pro KS Axtinguisher(~7.5 Keys)(21 Keys total)

http://backpack.tf/profiles/76561198051430158#!/compare/1490313600/1490400000

Added 4 Keys for a Cloud 9 Wraith Wrap(29 Keys)(25 Keys total)

http://backpack.tf/profiles/76561198139691389#!/compare/1486944000/1487116800

http://backpack.tf/profiles/76561198139691389#!/compare/1486944000/1487116800

Sold for 23 Keys

http://backpack.tf/profiles/76561198109272505#!/compare/1487462400/1487548800

Sold for 20 Keys and ~1 Key in Sweets(21 Keys total)

http://backpack.tf/profiles/76561198318362837#!/compare/1489536000/1489622400

20-25.

Credits to Mindacos for finding the proof, all I did was make the actual suggestion.