Resuggestion, thanks to Xerogyf + Foamy for the info!

Sale 1:

https://backpack.tf/profiles/76561198267189538#!/compare/1560556800/1560643200

https://backpack.tf/profiles/76561198153426959#!/compare/1560643200/1560988800

Sold for 19 keys

sale 2:

https://backpack.tf/profiles/76561198078574457#!/compare/1565049600/1566345600

https://backpack.tf/profiles/76561198156263572#!/compare/1564704000/1566086400

Untrace

Sale 3:

https://backpack.tf/profiles/76561198067273531#!/compare/1567468800/1567555200

https://backpack.tf/profiles/76561198109506971#!/compare/1567382400/1567555200

Untrace

sale 4:

https://backpack.tf/profiles/76561198109506971#!/compare/1567555200/1567728000

https://backpack.tf/profiles/76561198320615503#!/compare/1567468800/1567555200

https://backpack.tf/profiles/76561198089253101#!/compare/1567468800/1567555200

Gambling?

Sale 5:

https://backpack.tf/profiles/76561198089253101#!/compare/1567555200/1567641600

https://backpack.tf/profiles/76561198205939253#!/compare/1567555200/1567641600

Bulk

Sale 6:

https://backpack.tf/profiles/76561198205939253#!/compare/1567641600/1567728000

https://backpack.tf/profiles/76561198318065526#!/compare/1567555200/1567728000

uhhh.... crates?

Sale 7:

https://backpack.tf/profiles/76561198113749386#!/compare/1565654400/1566000000

https://backpack.tf/profiles/76561198192118853#!/compare/1565481600/1566000000

Bulky

Sale 8:

https://backpack.tf/profiles/76561198336843743#!/compare/1566259200/1566432000

https://backpack.tf/profiles/76561198021055079#!/compare/1566345600/1566432000

QS

Sale 9:

https://backpack.tf/profiles/76561198180881762#!/compare/1565913600/1566000000

https://backpack.tf/profiles/76561198800049685#!/compare/1563840000/1568160000

Sold for Searing Fur-Lined(19)

Sale 20:

https://backpack.tf/profiles/76561198058244665#!/compare/1565654400/1566604800

https://backpack.tf/profiles/76561198186922501#!/compare/1566518400/1566604800

Bulky

Sale 21:

https://backpack.tf/profiles/76561198186922501#!/compare/1566950400/1567036800

https://backpack.tf/profiles/76561198102929530#!/compare/1566950400/1567036800

Bulk for shotgun

Sale 22:

https://backpack.tf/profiles/76561198267189538#!/compare/1562544000/1562630400

https://backpack.tf/profiles/76561198092970316#!/compare/1562544000/1563148800

Can only trace 8 keys...

Sale 23:

https://backpack.tf/profiles/76561198092970316#!/compare/1563148800/1563667200

https://backpack.tf/profiles/76561198213234076#!/compare/1563580800/1563667200

Sold for 15 keys

Sale 24:

https://backpack.tf/profiles/76561198213234076#!/compare/1563667200/1563753600

https://backpack.tf/profiles/76561198802802073#!/compare/1563667200/1563753600

Sold with ~4 keys in sweets for OF Brown Bomber

Bomber Mini:

https://backpack.tf/suggestion/5d7dc83bd381727b180d1270

Suggestion for 21.5 keys

total is 17.5 keys

Sale 25:

https://backpack.tf/profiles/76561198802802073#!/compare/1563667200/1563753600

https://backpack.tf/profiles/76561198295061570#!/compare/1563667200/1563753600

Sold with ~1 key in sweets for Aces Falkirk

use there

Sale 26:

https://backpack.tf/profiles/76561198295061570#!/compare/1563926400/1564012800

https://backpack.tf/profiles/76561198159656266#!/compare/1563840000/1564012800

Sold for 10 keys + 2 spells

Veil Mini:

https://backpack.tf/profiles/76561198063175935#!/compare/1563753600/1563840000

https://backpack.tf/profiles/76561198159656266#!/compare/1563753600/1563840000

Sold for ~4 keys

Muffler Mini:

https://backpack.tf/profiles/76561198295061570#!/compare/1564272000/1564358400

https://backpack.tf/profiles/76561198159799709#!/compare/1564185600/1564272000

Sold for ~2 keys

Total is ~16 keys

Sale 27:

https://backpack.tf/profiles/76561198159656266#!/compare/1564790400/1564876800

https://backpack.tf/profiles/76561198844183288#!/compare/1564790400/1564876800

Sold with ~2 keys in sweets for Steaming Rotation

Rotation Mini:

https://backpack.tf/suggestion/5d7d799267807219e025f5af

Suggestion for 19.5 keys

Total is 21.5 keys

Sale 28:

https://backpack.tf/profiles/76561198844183288#!/compare/1565049600/1565136000

https://backpack.tf/profiles/76561198069493147#!/compare/1564963200/1565049600

Bulky

sale 29:

https://backpack.tf/profiles/76561198069493147#!/compare/1565049600/1565136000

https://backpack.tf/profiles/76561198346743052#!/compare/1565049600/1565136000

Sold for Flies Private Eye + 3 keys

use there

Total sales @:

15, 16, 17.5, 19, 19, 21.5 keys

Xerogyf's Part:

New sales:

https://backpack.tf/profiles/76561198312480435#!/compare/1573430400/1573516800

https://bot.tf/stats/item?def=30128&q=5&ef=Miami+Nights&craft=1&aus=0&ks=0

Sold for 13 keys

X = 13

https://marketplace.tf/items/tf2/30128;5;u61

$26 / 1.82 = 14.3

$20 /1.76 = 11.4

$18.78 / 1.79 = 10.5

X = 14, 11 (x2)

Foamy's Part:

Based on the above I suppose the range could be stretched to 13-19