Using last month.

Sale 1:

Sold to a bot for 2 keys + ~0.5 keys in metal

Seller: https://backpack.tf/profiles/76561198295305088#!/compare/1560470400/1560556800

Buyer: https://backpack.tf/profiles/76561198334559541#!/compare/1560470400/1560556800

https://backpack.tf/item/4765643328

https://i.imgur.com/lrdEVlx.png - Bot.tf confirms

X = 2.5

Sale 2:

Sold to a bot for 2 keys + 27 ref

Seller: https://backpack.tf/profiles/76561198873998676#!/compare/1559347200/1559433600

Buyer: https://backpack.tf/profiles/76561198817510262#!/compare/1559260800/1559347200

https://backpack.tf/item/3595541256

X = 2.5

Sale 3:

Sold for Buds (~2.5) + Pink Tossle (~0.5)

Seller: https://backpack.tf/profiles/76561198396322888#!/compare/1560470400/1560556800

Buyer: https://backpack.tf/profiles/76561198152350606#!/compare/1560470400/1560556800

https://bot.tf/stats/listings/M120DL74 - B/O of ~2.5 (after rounding to nearest .5)

https://backpack.tf/item/3595541256

X = 2.5 (Capped by B/O, rounded)

Other Sales:

https://backpack.tf/item/6789282196 (#1-3, excluded the gambling)

https://backpack.tf/item/6125365963 (#4, excluded the gambling)

https://backpack.tf/item/4765643328 (#5)

https://backpack.tf/item/3595541256 (#6 & #7)

https://backpack.tf/item/3451126351 (#8)

https://backpack.tf/item/3351886692 (#9, also an untraceable purchase that shows up on bot.tf)

https://backpack.tf/item/3218099422 (#10)

https://backpack.tf/item/5554925178 - marketplace

https://backpack.tf/item/3138821589 - gambled/marketplace

#1

Untraceable

https://backpack.tf/profiles/76561198136511793#!/compare/1558915200/1559001600

https://backpack.tf/profiles/76561198454615761#!/compare/1558915200/1559001600

https://i.imgur.com/lrdEVlx.png - labelled as a 2 key + 27 ref purchase

#2

Untraceable

https://backpack.tf/profiles/76561198454615761#!/compare/1559779200/1559865600

https://backpack.tf/profiles/76561198186823753#!/compare/1506729600/1559952000

#3

Untraceable

https://backpack.tf/profiles/76561198033661509#!/compare/1560038400/1560124800

https://backpack.tf/profiles/76561198357093059#!/compare/1560124800/1560211200

Most likely missing a person in the history

#4

Untraceable

https://backpack.tf/profiles/76561198334559541#!/compare/1560297600/1560384000

https://backpack.tf/profiles/76561198808491688#!/compare/1560297600/1560384000

https://i.imgur.com/lrdEVlx.png - Labelled as 2 keys + 39 ref, only 38 ref matches here.

#5

Untraceable

https://backpack.tf/profiles/76561197972383519#!/compare/1560384000/1560470400

https://backpack.tf/profiles/76561198295305088#!/compare/1560384000/1560470400

#6

Untraceable

https://backpack.tf/profiles/76561198963003558#!/compare/1558915200/1559001600

https://backpack.tf/profiles/76561198454615761#!/compare/1558915200/1559001600

https://i.imgur.com/lrdEVlx.png - labelled as a 2 key + 27 ref purchase, only 2 keys match. Ref may have been spent on keys

#7

Untraceable

https://backpack.tf/profiles/76561198000091310#!/compare/1560470400/1560556800

https://backpack.tf/profiles/76561198396322888#!/compare/1560470400/1560556800

#8

SCM

https://backpack.tf/profiles/76561198392655697#!/compare/1559433600/1559606400

https://backpack.tf/profiles/76561198307335196#!/compare/1559001600/1559779200

#9

Untraceable

https://backpack.tf/profiles/76561198037674114#!/compare/1559088000/1560124800

https://backpack.tf/profiles/76561198454615761#!/compare/1559088000/1559174400

#10

Untraceable

https://backpack.tf/profiles/76561198199926962#!/compare/1560038400/1560124800

https://backpack.tf/profiles/76561198357093059#!/compare/1560124800/1560211200

Sellers:

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

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

https://backpack.tf/item/4292051763 - ~2.7 keys

https://backpack.tf/item/6789282196 - ~2.7 keys

https://backpack.tf/item/3218099422 - ~2.7 keys

https://backpack.tf/item/4765643328 - ~2.8 keys

https://backpack.tf/item/3351886692 - ~3.4 keys

https://backpack.tf/item/3463308733 - 5 keys

Sales at:

2.5 (3x)

Excluded marketplace sales as they are not needed, and are usually way too high for taunts this low anyways.

The 4 listed for less than 3 keys would support the exclusion of anything that rounds to 3.

Going with 2.5 flat.