The sales used in the previous suggestion are now outdated.

Sales

Sale 1: Sold for 17 keys

https://backpack.tf/profiles/76561198271915998#!/compare/1598918400/1599004800

https://backpack.tf/profiles/76561198050052801#!/compare/1598745600/1599004800

Sale 2: Untrace

https://backpack.tf/profiles/76561198050052801#!/compare/1599609600/1600041600

https://backpack.tf/profiles/76561198091502579#!/compare/1599955200/1600041600

Sale 3: Untrace

https://backpack.tf/profiles/76561198091502579#!/compare/1600473600/1600560000

https://backpack.tf/profiles/76561198316159220#!/compare/1600214400/1600646400

Sale 4: Bulk

https://backpack.tf/profiles/76561198271915998#!/compare/1598572800/1598659200

https://backpack.tf/profiles/76561198056813536#!/compare/1598659200/1598745600

Marketplace

https://marketplace.tf/items/tf2/108;5;u88

September

$40 on September 19 (40/1.87 = 21~)

https://marketplace.tf/items/tf2/5021;6

https://manic.tf/keyprice/?at=2020-09-19

59.99 on September 20 (59.99/1.85 = 32~)

https://marketplace.tf/items/tf2/5021;6

https://manic.tf/keyprice/?at=2020-09-20

Classifieds

https://gyazo.com/1c5416514747ca05a2ae2bc3407d1040

Summary

Sales at 17.

Marketplace sales at 21 and 32.

Conclusion

32 seems high compared to the other sales, going to exclude it.

Going with 17-21 here.