(I just found out, anything above 30 keys should be rounded to the nearest key, and I was using the wrong marketplace.tf link...)

Strange Cosmic Calamity War Paint (Factory New)

https://steamcommunity.com/market/listings/440/Strange%20Cosmic%20Calamity%20War%20Paint%20%28Factory%20New%29

Dividing by the average price of a key on that day.

2 sold on January 16th, 2020:

$51.37/$2.45 = 20.97 ~ 21 keys

1 sold on January 20th:

$42.47/$2.44 = 17.41 ~ 17.4 keys

1 sold on January 21st:

$75.18/$2.42 = 31.07 ~ 31 keys

1 sold on February 19th:

$72.60/$2.38 = 30.5 ~ 31 keys

2 sold on March 26th:

$48.08/$2.15 = 22.36 ~ 22.4 keys

https://marketplace.tf/items/tf2/17225;11;w1;pk225

No recent sales so far this year.

Outlier: 17.4 keys.

Taking 21 - 31 keys as the range.