Sale 1:

Sold for Spec. KS Aussie Black Box (17) + Spec. KS Aussie Force-a-Nature (12)

http://www.tf2outpost.com/trade/28199931 - B/O of 29

Seller: http://backpack.tf/profiles/76561198059098316#!/compare/1465257600/1465430400

Buyer: http://backpack.tf/profiles/76561198145978386#!/compare/1462924800/1465344000

X = 29

Sale 2:

Sold for Smoking Company Man

No outpost

Seller: http://backpack.tf/profiles/76561198227073684#!/compare/1465948800/1466035200

Buyer: http://backpack.tf/profiles/76561198119563409#!/compare/1465948800/1466035200

X = 23

Sale 3:

Sold for 21 keys

http://www.tf2outpost.com/trade/28309884 --> http://www.tf2outpost.com/trade/28328872 - B/O of 21

Seller: http://backpack.tf/profiles/76561198070635520#!/compare/1468108800/1468195200

Buyer: http://backpack.tf/profiles/76561198301869691#!/compare/1468108800/1468195200

X = 21

Sellers:

24 keys:

http://puu.sh/q0jSV/e56283d7ce.png

25 keys:

http://puu.sh/q0jUy/2caaeccc0d.png - 12 days

http://puu.sh/q0jVf/265d336215.png - 3 days

27 keys:

http://puu.sh/q0jWe/03e69b7455.png - 3 days

Sales at:

21

23

29

Sale at 29 looks like a bit of an outlier, even though it sold for aussies, due to the current sellers at less than 29. Excluding 29

Going with 21-23