Challenge 19, Team F.L.A.M.B.E.S!

82nd suggestion, made by Beaser!

https://marketplace.tf/items/tf2/247;5;u7

$28.9 / $1.82 = 15.88 keys

$30 / $1.87 = 16.04 keys

https://backpack.tf/item/232076807

https://backpack.tf/item/359663519

Sale #1 -

FoD Rancho (14) + 2 keys

https://backpack.tf/profiles/76561198204215085#!/compare/1590192000/1590451200

https://backpack.tf/profiles/76561199014069450#!/compare/1590451200/1590537600

Sale #2 -

QS

https://backpack.tf/profiles/76561198151531499#!/compare/1589760000/1589932800

https://backpack.tf/profiles/76561198204215085#!/compare/1589500800/1590192000

Taking 16 flat!

FoD Ranch Mini:

Taking valid mp sales

https://marketplace.tf/items/tf2/1115;5;u3005

$22 / $1.99 = 11.06 keys

$25 / $1.99 = 12.56 keys

$25 / $1.98 = 12.63 keys

$25 / $2.01 = 12.44 keys

$27.72 / $1.94 = 14.29 keys

$27.72 / $1.91 = 14.51 keys

$29 / $1.87 = 15.51 keys

$29 / $1.89 = 15.34 keys

$29 / $1.89 = 15.34 keys

$29 / $1.90 = 15.26 keys

$29 / $1.90 = 15.26 keys

$29.69 / $1.77 = 16.77 keys

$29.69 / $1.72 = 17.26 keys

Excluding 11, 16, and 17, taking 13 - 15