Steaming + Tyrolean = Styro-Foam

https://backpack.tf/item/724617521

Sale 1) Sold for $22.22 when Keys were ~$1.68 each

https://marketplace.tf/items/101;5;u36

https://marketplace.tf/items/5021;6/Mann%20Co.%20Supply%20Crate%20Key

22.22 / 1.68 = 13.23, which rounds to 13 Keys

https://backpack.tf/item/1356237529

Sale 2) ?

https://backpack.tf/profiles/76561198044690674#!/compare/1534032000/1539820800

Sale 3) Sold for 13 Keys

https://backpack.tf/profiles/76561198053252981#!/compare/1544054400/1544140800

Sale 4) ?

https://backpack.tf/profiles/76561198078178141#!/compare/1544313600/1545436800

Sale 5) ?

https://backpack.tf/profiles/76561198337734785#!/compare/1544745600/1544832000

https://backpack.tf/profiles/76561198109717465#!/compare/1544745600/1544832000

https://backpack.tf/item/471012128

Sale 6) ?

https://backpack.tf/profiles/76561198315588518#!/compare/1539302400/1539388800

Sale 7) Sold for 13 Keys

https://backpack.tf/profiles/76561198021272428#!/compare/1541289600/1541376000

IDs match.

Sale 8) ?

https://backpack.tf/profiles/76561198078178141#!/compare/1541462400/1543449600

Sale 9) ?

https://backpack.tf/profiles/76561198312583107#!/compare/1541548800/1541635200

Sale 10) ?

https://backpack.tf/profiles/76561197997268820#!/compare/1541980800/1542067200

https://backpack.tf/profiles/76561198797908236#!/compare/1541980800/1542067200

Sale 11) ?

https://backpack.tf/profiles/76561198797908236#!/compare/1542240000/1542326400

Sale 12) ?

https://backpack.tf/profiles/76561198312583107#!/compare/1543017600/1543104000

https://backpack.tf/profiles/76561198075318283#!/compare/1543017600/1543104000

Sale 13) Sold for a Strange '72 Burstchester

https://backpack.tf/profiles/76561198075318283#!/compare/1543190400/1543276800

Low outlier.

Sale 14) Bulk sale

https://backpack.tf/profiles/76561198000247762#!/compare/1544140800/1544400000

Sale 15) Bulk sale

https://backpack.tf/profiles/76561198072355915#!/compare/1544313600/1544400000

https://backpack.tf/profiles/76561198092970316#!/compare/1544400000/1544572800

https://marketplace.tf/items/101;5;u36 - Sold for $22.50 when Keys were ~$1.76 each

https://marketplace.tf/items/5021;6/Mann%20Co.%20Supply%20Crate%20Key

22.5 / 1.76 = 12.78, which rounds to 13 Keys