2 sellers for 16 keys (one says 15 pure in comments :/) Listed less than half a week since this suggestion.

2 incredibly old post on bazaar.tf:

https://bazaar.tf/trade/1530998 (private inventory, but snapshot 6 months ago says unusual was sold)

https://bazaar.tf/trade/1550567(sold for indeterminate amount in july)

Outpost has one listing

http://www.tf2outpost.com/search/272991893 (selling for 15 pure)

Sale 1:

https://backpack.tf/profiles/76561198292513121#!/compare/1516233600/1516406400 Buyer

https://backpack.tf/profiles/76561198398538326#!/compare/1516233600/1516665600 Seller

Sold for 10 pure + 35.66 sweets (Seller immediately spent keys on Banana Hat)

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Sale 2:

https://backpack.tf/profiles/76561198203443358#!/compare/1516406400/1516492800

Sold for Purple Fetti Herald's Helm + 1 key pure

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PF Helm Mini:

https://backpack.tf/profiles/76561198126542743#!/compare/1516233600/1516492800 Buyer

https://backpack.tf/profiles/76561198208062409#!/compare/1516406400/1516492800 Seller

Sold with a key for Orbiting Fire Milkman(13.5).

14.5 total.

https://backpack.tf/profiles/76561198167529655#!/compare/1516665600/1516752000 Seller

https://backpack.tf/profiles/76561198129586174#!/compare/1516665600/1516752000 Buyer

Sold for Smoking Hottie's Hoodie + Spec KS MW Liquid Asset Sticky Launcher (2 keys)*

14+(2 to 5)= 16 to 19. pricing at lowest due to current amount.

*Note that on SCM the sticky was worth closer to 5 keys at the time of the sale.

Only 2 recent sales, average at (16+ 14.5)/2 = 15.25 keys.

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Sale 3:

https://backpack.tf/profiles/76561198304138933#!/compare/1515024000/1515196800 Seller

https://backpack.tf/profiles/76561198086844082#!/compare/1514592000/1515110400 Buyer

Bought for 16 pure from bot.

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so thats: 10.97 keys

16 keys

16.25 keys

10.97 is outlier (quicksell), so price stays at 16.