looking at the last few months (july until now of me creating this suggestion) (https://marketplace.tf/items/tf2/5021;6 < keys) (https://marketplace.tf/items/tf2/31091;5;u138 < the hat)

Marketplace.tf sales:

First sale on marketplace went for $130 usd https://imgur.com/a/oA9cZKB

keys price that day im unable to see closest one is key prices on july 14 with keys going for $1.93 usd https://imgur.com/a/8QMJ628

taking 130 divided by 1.93 gives u 67.35 and rounding down to 67 keys

Second sale on marketplace went for $130 usd https://imgur.com/a/i1vi17W

keys price that day going for $1.95 usd https://imgur.com/a/s17se8J

taking 130 divided by 1.95 gives u 66.66 and rounding that up to 67

Third sale on marketplace went for $154.99 https://imgur.com/a/Qnjb30V

keys price that day going for $1.85 usd https://imgur.com/a/YGt1CkN

taking 154.99 and dividing by 1.85 gives u 83.77 and rounding that up to 84

Fourth sale on marketplace went for $152.99 usd https://imgur.com/a/0ZADHgv

keys price that day going for $1.89 usd https://imgur.com/a/RTLcy1Y

taking 152.99 and dividing by 1.89 gives u 80.94 and rounding that up to 81

Other sales on different sites:

Sale on scrap.tf went for 40 keys flat https://imgur.com/a/H70VDa0

40,67,67,81,84

getting rid of 40 since its below buy orders. (https://backpack.tf/stats/Unusual/Citizen%20Cane/Tradable/Craftable/138 < to check the current buy orders)

if there were more sales please list them in comments and ill do another suggestion! this is also my first real suggestion.