Using last month.

Sales 1-3:

Sold for $41.99, $44.99, & $34 on marketplace.tf

https://marketplace.tf/items/1115;5;u3001

https://backpack.tf/item/7104730366 - no outpost

https://backpack.tf/item/4967503379 - no outpost

https://backpack.tf/item/6894580626 - no outpost

http://manic.tf/keyprice/?at=2018-08-28 - $41.99 / $1.88 = 22.34 keys

http://manic.tf/keyprice/?at=2018-09-02 - $44.99 / $1.88 = 23.93 keys

http://manic.tf/keyprice/?at=2018-09-11 - $34 / $1.87 = 18.18 keys

X = 24

X = 22

X = 18

Sale 4:

Sold for 14 keys + 20 ref

Seller: https://backpack.tf/profiles/76561198100344879#!/compare/1534464000/1534636800

Buyer: https://backpack.tf/profiles/76561198030481057#!/compare/1534550400/1534636800

https://backpack.tf/item/2891620207

X = 15

Sale 5:

Sold for 14 keys + 3 ref

Seller: https://backpack.tf/profiles/76561198030481057#!/compare/1534723200/1534809600

Buyer: https://backpack.tf/profiles/76561198079413347#!/compare/1534723200/1534809600

https://backpack.tf/item/2891620207

X = 14

Other Sales:

https://backpack.tf/item/7104730366 (#1-4)

https://backpack.tf/item/4126735310 (#5)

https://backpack.tf/item/3390775906 (#6-9)

https://backpack.tf/item/2780266836 (#10)

https://backpack.tf/item/5791901010 (#11)

https://backpack.tf/item/6207705959 (#12 & #13)

https://backpack.tf/item/3928744553 - tf2mart stuff

#1

Bulk for unusual revolver

https://backpack.tf/profiles/76561198328835671#!/compare/1535760000/1535846400

https://backpack.tf/profiles/76561198003926663#!/compare/1535760000/1535846400

#2

Probably bulk or something

https://backpack.tf/profiles/76561198003926663#!/compare/1536278400/1536364800

https://backpack.tf/profiles/76561198410429966#!/compare/1536278400/1536364800

#3

Bulk or gambled

https://backpack.tf/profiles/76561198410429966#!/compare/1536278400/1536364800

https://backpack.tf/profiles/76561198112964569#!/compare/1536105600/1536364800

#4

Probs gambled

https://backpack.tf/profiles/76561198112964569#!/compare/1536364800/1536537600

https://backpack.tf/profiles/76561198044010685#!/compare/1536451200/1536537600

#5

Untraceable

https://backpack.tf/profiles/76561198109904696#!/compare/1537056000/1537142400

https://backpack.tf/profiles/76561198312583107#!/compare/1536969600/1537056000

https://i.imgur.com/H4ZaNH7.png - Labelled as 13 keys + 6 ref

#6

Bulk for unusual scattergun

https://backpack.tf/profiles/76561198041889097#!/compare/1529625600/1534809600

https://backpack.tf/profiles/76561198063640894#!/compare/1534723200/1534809600

#7

Sold for 12 keys + Infernal Smoke Battin’ + Fountain of Delight Headcase

https://backpack.tf/profiles/76561198063640894#!/compare/1535414400/1535500800

https://backpack.tf/profiles/76561198074438385#!/compare/1535500800/1535587200

No outpost, gonna be way too high without a B/O cap.

#8

Sold with 4 keys for Grail Luxury Lounge

https://backpack.tf/profiles/76561198074438385#!/compare/1535760000/1535846400

https://backpack.tf/profiles/76561198003926663#!/compare/1535760000/1535846400

Should be used on the lounge.

#9

Probably gambled

https://backpack.tf/profiles/76561198003926663#!/compare/1535760000/1535846400

https://backpack.tf/profiles/76561198065761144#!/compare/1535760000/1535846400

#10

Untraceable

https://backpack.tf/profiles/76561198150253697#!/compare/1534118400/1534291200

https://backpack.tf/profiles/76561198334598690#!/compare/1534032000/1534118400

https://i.imgur.com/H4ZaNH7.png - labelled as 14 keys

#11

Untraceable

https://backpack.tf/profiles/76561198151315394#!/compare/1533427200/1533600000

https://backpack.tf/profiles/76561198311498888#!/compare/1533772800/1533859200

Probably scammed

#12

https://backpack.tf/profiles/76561198078457532#!/compare/1533859200/1534291200

https://backpack.tf/profiles/76561198825959809#!/compare/1534204800/1534291200

#13

Untraceable

https://backpack.tf/profiles/76561198335791307#!/compare/1534204800/1534291200 - private backpack

https://backpack.tf/profiles/76561198335791307#!/compare/1534204800/1534291200

https://i.imgur.com/H4ZaNH7.png - labelled as 14 keys

Sellers:

https://i.imgur.com/za5xYuq.png

https://i.imgur.com/Qwka7GZ.png

https://backpack.tf/item/4126735310 - ~16.56 keys

https://backpack.tf/item/3827158524 - ~16.73 keys

https://backpack.tf/item/6207705959 - 17 keys

https://backpack.tf/item/6550492218 - 17 keys

https://backpack.tf/item/2780266836 - 17 keys

https://backpack.tf/item/3314858191 - 19 keys

https://backpack.tf/item/6663329810 - 26 keys

https://backpack.tf/item/2720659167 - 80 keys

https://backpack.tf/item/2690642332 - 84 keys

Sales at:

14

15

18

22

24

18+ are all too high, given 5 sellers less than 18. Excluding 18+.

Going with 14-15.

https://backpack.tf/item/6771263764 - tf2mart/scammers

https://backpack.tf/item/5825300621 - not unusual at the time

sold for 15 keys

https://backpack.tf/profiles/76561198097271466#!/compare/1537920000/1538006400

https://backpack.tf/profiles/76561198148511293#!/compare/1537920000/1538006400

https://backpack.tf/item/3827158524

https://backpack.tf/profiles/76561198148511293#!/compare/1537920000/1538006400

https://backpack.tf/profiles/76561198198245779#!/compare/1537574400/1538265600

sold for purple confetti aztec aggressor, way too low probably

some sellers have dropped their prices:

https://i.imgur.com/j6S1zAY.png