This Mini chain is brutal.

https://backpack.tf/item/273478359

Sale 1) Sold for a Vivid Plasma Defiant Spartan (30 Keys) + ~6 Keys of Items

https://backpack.tf/profiles/76561198411126009#!/compare/1505520000/1505606400

30 + 6 = 36 Keys

Sale 2) Sold + 3 Keys + ~2 Keys of Items for a Searing Plasma Modest Pile of Hat (42 Keys)

https://backpack.tf/profiles/76561198080347917#!/compare/1506988800/1507075200

42 - 3 - 2 = 37 Keys

Modest Mini

https://backpack.tf/profiles/76561198060597356#!/compare/1505088000/1505174400 - Sold for a Circling Heart Fancy Fedora (42 Keys)

Fedora Micro

https://backpack.tf/suggestion/59b8693dcf6c752483160d51 - Taking 42 Keys, as that would have been valid had sin resuggested when Mindacos commented

https://backpack.tf/item/6191255197

Sale 3) Sold for a Duped Green Energy Fed-Fightin' Fedora (44.5 Keys)

https://backpack.tf/profiles/76561198403902482#!/compare/1507248000/1507334400

Rounds to 45 Keys

Fedora Mini

https://backpack.tf/profiles/76561198159149142#!/compare/1506902400/1506988800 - Sold for an Orb. Fire Honcho's + CPS Conquistador + Steaming MYB

http://www.tf2outpost.com/trade/29387450 - Capped by the Buyout of 53 Keys

https://backpack.tf/profiles/76561198403902482#!/compare/1507507200/1507593600 - Sold for a C9 Tam + KaW Crocleather + ~1 Key of Items

https://backpack.tf/profiles/76561198069740698#!/compare/1508716800/1508803200 - Sold + 7 Keys for a Blizzardy Trophy + Orb. Fire Dread Hiding

https://backpack.tf/profiles/76561198023476204#!/compare/1509494400/1509580800 - Sold + WW Cool Blitzkrieg Revolver for a Secret Mining Light

The Tam sale is roughly 36 Keys, the first sale is 53 Keys, and the other 2 fall in the middle (the Dread has a 29 Key Seller). I'll take the wide range of 36 - 53 Keys

Dread Micro

https://imgur.com/a/jXdLX - 29 Key Seller

Sale 4) Sold for a Duped Green Energy Grenadier's Softcap (30 Keys)

https://backpack.tf/profiles/76561198148833495#!/compare/1508544000/1508716800

Softcap Mini

https://backpack.tf/profiles/76561198139476358#!/compare/1508112000/1508371200 - Sold for a Cloud 9 Lucky Shot (29 Keys)

https://backpack.tf/profiles/76561198148833495#!/compare/1509235200/1509321600 - Sold for a Haunted Ghosts Drill Hat (30 Keys) + 1 Key

https://backpack.tf/profiles/76561198127018137#!/compare/1507507200/1509753600 - The Drill above was bought for 30 Keys and sold the same day.

Sale 5) Bulk sale for an Eldritch Flame Prehistoric Pullover

https://backpack.tf/profiles/76561198113394590#!/compare/1508716800/1508803200 - Buyer's Backpack

Sale 6) Bulk sale for an Ancient Eldritch Prehistoric Pullover

https://backpack.tf/profiles/76561198113394590#!/compare/1508803200/1508976000

Sale 7) Bulk sale for a Neutron Star Crone's Dome

https://backpack.tf/profiles/76561198084976847#!/compare/1509148800/1509321600

Sale 8) Sold for an Infernal Flames Zoomin' Broom

https://backpack.tf/profiles/76561198156255538#!/compare/1509753600/1509840000

This sale should be used to update the Broom or be excluded from this and that as an Outlier.

Rounding 36 down to 35 Keys for a nice 35 - 45 range. The 30 Key sale is a low Outlier because of this Buyer at 32 Keys: https://imgur.com/a/9dJMh