Sale #1:

https://marketplace.tf/items/30919;5;u3006

Sold for $35 on February 17, 2019.

$35 / $1.79 = ~19.6 keys

20 keys

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Sale #2:

https://marketplace.tf/items/30919;5;u3006

Sold for $22 on February 16, 2019.

$22.00 / $1.80 = ~12 keys

12 keys

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Sale #3:

https://marketplace.tf/items/30919;5;u3006

Sold for $29.99 on January 25, 2019.

$29.99 / $1.77 = ~17 keys

17 keys

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Sale #4:

https://marketplace.tf/items/30919;5;u3006

Sold for $25 on December 18, 2019.

$25 / $1.64 = ~15.2 keys

15 keys

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Sale #5:

https://backpack.tf/profiles/76561197970657444#!/compare/1548028800/1550275200

SCM Sale.

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Sale #6:

https://backpack.tf/profiles/76561198343986638#!/compare/1543017600/1550620800

Untracable.

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Sale #7:

https://backpack.tf/profiles/76561198155699667#!/compare/1550361600/1550448000

Bulk.

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Sale #8:

https://backpack.tf/profiles/76561198044684270#!/compare/1548028800/1548115200

Unsure.

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Sale #9:

https://backpack.tf/profiles/76561198027458189#!/compare/1550361600/1550448000

Untracable.

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Sale #10:

https://backpack.tf/profiles/76561198114402400#!/compare/1550016000/1550102400

Sold for 17 keys.

17 keys

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Sale #11:

https://backpack.tf/profiles/76561198101162889#!/compare/1548374400/1548547200

Untracable.

Seller at 17 keys for one month (https://i.imgur.com/8j3MYzr.png) shows 17 keys is too high. Going with 12 - 15 keys.