Sale 1: (This sale occurred as soon as I was done suggesting)

Sold for 31 keys + ~1 key in ref

http://i.imgur.com/d2WCzQy.png - B/O of 36

Seller: https://backpack.tf/profiles/76561198132226518#!/compare/1503360000/1503446400

Buyer: https://backpack.tf/profiles/76561198256138546#!/compare/1503360000/1503446400

X = 32

Sale 2:

Sold with 2 keys for Steaming Soldier's Stash (Suggestion at 32.5)

http://i.imgur.com/A6zxWrJ.png - B/O of 36

Seller: https://backpack.tf/profiles/76561198087172601#!/compare/1501977600/1502064000

Buyer: https://backpack.tf/profiles/76561198260967101#!/compare/1501977600/1502064000

X = 31

Sale 3:

Quicksold for 27 keys

No outpost

Seller: https://backpack.tf/profiles/76561198243076082#!/compare/1502409600/1502496000

Buyer: https://backpack.tf/profiles/76561198143516878#!/compare/1502409600/1502496000

X = 27

Sale 4:

Quicksold for 27 keys on scrap.tf auctions

Seller: https://backpack.tf/profiles/76561198197287330#!/compare/1502755200/1502841600

Buyer: https://backpack.tf/profiles/76561198114831089#!/compare/1502755200/1502841600

X = 27

Sale 5:

Quicksold for 26 keys

No outpost

Seller: https://backpack.tf/profiles/76561198042773083#!/compare/1502236800/1502323200

Buyer: https://backpack.tf/profiles/76561198269304492#!/compare/1502064000/1502323200

X = 26

Sale 6:

Quicksold for 25 keys + <0.5 keys in items

No outpost

Seller: https://backpack.tf/profiles/76561198269304492#!/compare/1502323200/1502409600

Buyer: https://backpack.tf/profiles/76561198243076082#!/compare/1502323200/1502409600

X = 25

Sale 7:

Sold for Molten Mallard Baron von Havenaplane

http://www.tf2outpost.com/trade/29330017 - No visible B/O

Seller: https://backpack.tf/profiles/76561198193710729#!/compare/1502755200/1502841600

Buyer: https://backpack.tf/profiles/76561198197287330#!/compare/1502755200/1502841600

Not many valid sales on the Baron that aren't quicksales, probably best to use this on the baron instead.

Sale 8:

Sold for 18 keys + Duelling minigames?

Seller: https://backpack.tf/profiles/76561198260967101#!/compare/1502841600/1502928000

Buyer: https://backpack.tf/profiles/76561198193710729#!/compare/1502755200/1502841600

If the sale is correct, it's countered by buyers.

Sale 9:

Bulk for Sulphurous Valley Forge

Seller: https://backpack.tf/profiles/76561198188596873#!/compare/1502668800/1502928000

Buyer: https://backpack.tf/profiles/76561198346118738#!/compare/1502841600/1502928000

Pretty bulky, don't wanna use this here.

Steaming Soldier's Stash:

https://backpack.tf/suggestion/599d6cf2cf6c753f1061cd09

Sellers:

34 keys:

http://www.tf2outpost.com/trade/29340914 - very, very young

http://i.imgur.com/dfbC5mv.png - 35 here

36 keys:

http://i.imgur.com/YoA4m4h.png - 3 days

Sales at:

25

26

27 (2x)

31

32

Was considering going with 27-31, using the quicksells as the low-end, as it was a very common trading point, but the new sale at 32 should make it alright to exclude 27 and lower.

http://www.tf2outpost.com/trade/29330017 - 30 offered here, the dude that offered was the dude that bought it in sale 1.

Going with 31-32.