Turns out I priced this wrong, someone added me and gave me a sale that didn’t show up in the histories.

Sale 1: (outlier)

Sold for 12 keys, a Pro Back Scratcher and a Pro Neon Annihilator

(12 + 3 + 2) = 17 keys

http://backpack.tf/profiles/76561197961067008?time=1429254000 (April 17th)

http://backpack.tf/profiles/76561197961067008?time=1429340400 (April 18th)

Sale 2: (outlier)

Sold for an Aces High Human Cannonball

(17.5*0.9) = 15.75 rounding to 16 keys

http://backpack.tf/profiles/76561198047793562?time=1427785200 (March 31st)

http://backpack.tf/profiles/76561198047793562?time=1427871600 (April 1st)

Sale 3: (outlier)

Sold for a Steaming Surgeon's Shako

(21.5*0.9) = 19.35 rounding to 19 keys

http://backpack.tf/profiles/76561198047793562?time=1427439600 (March 27th)

http://backpack.tf/profiles/76561198047793562?time=1427785200 (March 31st)

Sale 4:

Sold for a Steaming Executioner

28 keys

http://backpack.tf/profiles/76561198064745482?time=1428649200 (April 10th)

http://backpack.tf/profiles/76561198064745482?time=1428735600 (April 11th)

Sale 5:

Sold for 31 keys

http://pokit.org/get/?a9151cc9fbf2f317a6dffd705637cc96.jpg

Notes:

Mini for the Pro Back Scratcher

1 seller at $6.50

(6.5/2.4) = 2.70833333 rounding to 3 keys

http://steamcommunity.com/market/listings/440/Strange%20Professional%20Killstreak%20Back%20Scratcher

Mini for the Pro Neon Annihilator

1 seller at $5.75

(5.8/2.4) = 2.41666667 rounding to 2 keys

http://steamcommunity.com/market/listings/440/Strange%20Professional%20Killstreak%20Neon%20Annihilator

Mini for the Steaming EXE

Only 2 recent sales I can find

(41.5*0.9) - 11 = 26.35 rounding to 26 keys

http://backpack.tf/profiles/76561198067556635?time=1427612400 (March 29th)

http://backpack.tf/profiles/76561198067556635?time=1427698800 (March 30th)

http://www.tf2outpost.com/trade/25723979

QS for 28 keys

Taking the price at 28 keys

Conclusion:

Taking the final range at 31 to 28 as those are the most recent sales.