3 year old price...

https://backpack.tf/item/4014584969

Sold for a Green Confetti Coldsnap Cap (median key price: 15 keys 2 weeks ago) + 3 keys 12 ref

Total of 18 keys 12 ref, 18.25 keys ~18 keys

https://backpack.tf/profiles/76561198059098316#!/compare/1597536000/1597622400

https://backpack.tf/profiles/76561198330231701#!/compare/1597363200/1597622400

Untrace

https://backpack.tf/profiles/76561198026129220#!/compare/1591920000/1592006400

https://backpack.tf/profiles/76561198059098316#!/compare/1591920000/1592006400

Untrace:

https://backpack.tf/profiles/76561198076020691#!/compare/1591833600/1592006400

https://backpack.tf/profiles/76561198026129220#!/compare/1591833600/1591920000

Marketplace.tf sales:

(PRO KS) https://marketplace.tf/items/tf2/15058;15;u703;w2;pk58;kt-3

June 23 2020: $39.99 (key=$2.00, 20 keys)

(UNTRACEABLE)

The Pro ks sale is fairly close to the non ks sale so I'll include it too, them being the only 2 recent sales

Going with 18-20 keys