gonna take this over since the previous person never responded I guess

(credit to Erebus)

Marketplace

https://marketplace.tf/items/tf2/30984;5;u12

https://backpack.tf/item/6771903901

$17.99 / $1.78 = 10.11 keys

Mannco store

https://mannco.store/item/440-massed-flies-unusual-sky-high-fly-guy

https://backpack.tf/item/6748677059

$18 / $1.62 = 11.11 keys

(Credit to Shuffle Spy)

https://backpack.tf/item/6739376583 - This was actually the history of the Marketplace sale

https://backpack.tf/profiles/76561198041381757#!/compare/1647820800/1647907200 - Bulk sale

https://backpack.tf/profiles/76561199150584182#!/compare/1647993600/1648080000 - Quicksold for 8 Keys + 35.66 Refined

https://imgur.com/a/j1iuVMj - There are 2 for sale on the community market for 9 Keys

https://gladiator.tf/time-machine?item=Massed+Flies+Sky+High+Fly+Guy&at=2022-06-07T23%3A49%3A00.000Z - Seller for 3 months at 10 Keys

11 will be too high because of how long the seller at 10 has been listed for.

While buyers are at 9 Keys, the sale at 8.5 Keys and the 2 sellers at 9 Keys supports including 9 as the low end.

9 to 10 would work here.

https://backpack.tf/profiles/76561198086011812#!/compare/1656547200/1656633600 - Quicksold for 9 Keys

The ones on SCM also both sold.