Holy Five

https://backpack.tf/item/1310524775

Sale 1) Looks like an SCM sale

https://backpack.tf/profiles/76561198364730989#!/compare/1548979200/1549238400

https://backpack.tf/profiles/76561198262173913#!/compare/1548979200/1549497600

https://backpack.tf/item/2224943809

Sale 2) ?

https://backpack.tf/profiles/76561198085291131#!/compare/1547164800/1547251200

Sale 3) ?

https://backpack.tf/profiles/76561198353505010#!/compare/1550188800/1550275200

Sale 4) ?

https://backpack.tf/profiles/76561198305676157#!/compare/1551484800/1551571200

https://backpack.tf/profiles/76561198403404710#!/compare/1551484800/1551571200

https://backpack.tf/item/4479568052

Sale 5) Sold for 10 Keys + 0.33 Refined

https://backpack.tf/profiles/76561198399031554#!/compare/1547769600/1547942400

Low outlier.

Sale 6) Think this is a Marketplace sale

https://backpack.tf/profiles/76561198023051867#!/compare/1548028800/1548115200

https://backpack.tf/profiles/76561198126461177#!/compare/1548806400/1549065600

https://backpack.tf/item/4958324356

Sale 7) Sold for 13 Keys

https://backpack.tf/profiles/76561198085921714#!/compare/1550448000/1550620800

https://backpack.tf/item/2642473331

Sale 8) ?

https://backpack.tf/profiles/76561198009872417#!/compare/1545955200/1550016000

https://backpack.tf/item/1364173257

Sale 9) ?

https://backpack.tf/profiles/76561198153991361#!/compare/1546560000/1546819200

Sale 10) Sold for 8 Keys

https://backpack.tf/profiles/76561198833008516#!/compare/1546646400/1546732800

Low outlier.

Sale 11) ?

https://backpack.tf/profiles/76561198371026030#!/compare/1546646400/1546732800

Sale 12) ?

https://backpack.tf/profiles/76561198080706417#!/compare/1547942400/1548115200

https://backpack.tf/profiles/76561198371026030#!/compare/1547769600/1548115200

Sale 13) ?

https://backpack.tf/profiles/76561198371026030#!/compare/1547769600/1548115200

https://backpack.tf/profiles/76561198132504113#!/compare/1548201600/1548288000

Sale 14) ?

https://backpack.tf/profiles/76561198132504113#!/compare/1548547200/1548633600

https://backpack.tf/profiles/76561198844472460#!/compare/1548547200/1548633600

Sale 15) Sold for 11 Keys

https://backpack.tf/profiles/76561198844472460#!/compare/1548633600/1548720000

https://backpack.tf/profiles/76561198121385547#!/compare/1548633600/1548720000

Low outlier.

https://backpack.tf/item/5935060176

Sale 16) Sold for a Searing Plasma Screamin' Eagle (17 Keys)

https://backpack.tf/profiles/76561198336513007#!/compare/1547769600/1547942400

Eagle Mini

https://backpack.tf/suggestion/5c7c40b26780727c8d3d7319 - 17 Keys

Sale 17) ?

https://backpack.tf/profiles/76561198336513007#!/compare/1548201600/1548288000

https://backpack.tf/profiles/76561198297669075#!/compare/1548115200/1548201600

https://backpack.tf/item/635363003 - Was never Unusual

https://backpack.tf/item/4479568052

https://marketplace.tf/items/167;5;u3003 - Sold for $34.99 when Keys were ~$1.81 each

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

34.99 / 1.81 = 19.33, which rounds to 19 Keys

Since this took a month, I'm calling this a high outlier.