The burning rage I have right now for missing the Buyout Cap in the Something Burning This Way Comes Tosslecap suggestion I'm about to post.

http://backpack.tf/item/277398724

Sale 1) Sold + Stormy Storm A Hat to Kill For (25 Keys) + ~5 Keys of Items for a Duped Burning Flames Front Runner (180.5 Keys)

http://backpack.tf/profiles/76561198028274974#!/compare/1493683200/1493769600

180.5 - 25 - 5 = 150.5, which I'll round to 150 Keys

Front Runner Mini

Sold + Showstopper Skullcracker (66 Keys) + ~1 Key of Items for a Nebula Phononaut (247.5 Keys)

http://backpack.tf/profiles/76561198153088409#!/compare/1496102400/1496275200

247.5 - 66 - 1 = 180.5 Keys

A Hat to Kill For Mini

Sold for a Circling Peace Sign Ye Olde Baker Boy

http://backpack.tf/profiles/76561198180484678#!/compare/1494288000/1494374400

http://www.tf2outpost.com/trade/28965434 - Capped by the Buyout of 25 Keys

Sale 2) Sold for a Duped Sunbeams Milkman (60 Keys) + 60 Keys

http://backpack.tf/profiles/76561198355387742#!/compare/1496534400/1496620800 - Buyer's Backpack

60 + 60 = 120 Keys

Milkman Mini

Sold for an Australium Scattergun (23 Keys) + Vivid Milkman (22 Keys) + Nuts and Bolts Phantom

http://backpack.tf/profiles/76561198079757969#!/compare/1492819200/1492905600

http://www.tf2outpost.com/trade/28887792 - Capped by the Buyout of 60 Keys

Sale 3) Sold for a Poisoned Shadows Reggaelator (160 Keys) + Cats (23 Keys)

http://backpack.tf/profiles/76561198355387742#!/compare/1496793600/1496880000

160 + 23 = 183 Keys

Since there isn't much to disprove 120 or 183, I'll go 150 flat. The average of 120 - 183 is roughly 150 Keys as well.