52 Exist. 52

http://backpack.tf/item/524377726

Sale 1) Quicksold for 22 Keys

http://backpack.tf/profiles/76561198048008254#!/compare/1481328000/1481414400

Sale 2) Sold + 2 Keys + Conga (~0.5 Keys) for a Blizzardy Storm Surgeon's Stahlhelm

http://backpack.tf/profiles/76561198259809286#!/compare/1481673600/1481760000

http://www.tf2outpost.com/trade/28661112 - Capped by the Buyout of 24 Keys

Sale 3) Sold for 20-something-I-can't-tell Keys

http://backpack.tf/profiles/76561198048008254#!/compare/1481673600/1481760000

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http://backpack.tf/item/819885761

Sale 4) Sold for 20 Keys

http://backpack.tf/profiles/76561198070704045#!/compare/1475193600/1475280000

Sale 5) Sold + Duped Orbiting Planets Sergeant's Drill Hat for a Specialized Killstreak Australium Rocket Launcher

http://backpack.tf/profiles/76561198051515564#!/compare/1477785600/1477872000

http://www.tf2outpost.com/trade/28565602 - Capped by the Buyout of 28 Keys

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http://backpack.tf/item/830307513

Sale 6) Quicksold for 21 Keys

http://backpack.tf/profiles/76561198141170332#!/compare/1478736000/1478822400

Sale 7) Sold for 22 Keys

http://backpack.tf/profiles/76561198079230140#!/compare/1480723200/1480809600 - Buyer's Backpack

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http://backpack.tf/item/839614070

Sale 8) Sold for a Blizzardy Storm Noble Amassment of Hats

http://backpack.tf/profiles/76561198056753441#!/compare/1475884800/1475971200

Fits in the range.

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http://backpack.tf/item/1943779449

Sale 9) Sold for a Smoking Federal Casemaker

http://backpack.tf/profiles/76561198237327668#!/compare/1477526400/1477699200

http://www.tf2outpost.com/trade/28535055 - Capped by the Buyout of 30 Keys

Given the 2 sales at 28 and 30 Keys, I'm including 30 as the high end.

I'm also including 22 Keys despite the quicksell because there are two total sales at 22 Keys.