Sale 1 :

Before : http://backpack.tf/profiles/76561198167161932?time=1433055600

After : http://backpack.tf/profiles/76561198167161932?time=1433142000

Sold for an Electrostatic Broadband Bonnet : 13 * 0.9 : 12 keys

Mini on the bonnet : http://i.imgur.com/uLx714M.png

Sold for 10 keys pure + 3 keys in items : 13 keys

Sale 2 : (outlier)

Before : http://backpack.tf/profiles/76561197987181903?time=1432537200

After : http://backpack.tf/profiles/76561197987181903?time=1432623600

Sold for a Terror-Watt Magnificent Mongolian : 16 keys ( not applying overpay as mini is in pure )

Mini on the terror watt mongolian :

Before : http://backpack.tf/profiles/76561198123977468?time=1427612400

After : http://backpack.tf/profiles/76561198123977468?time=1427698800

Sold for a spec ks aussie sticky but 1 key in items was added : 17 - 1 = 16 keys

Sticky : http://steamcommunity.com/market/listings/440/Strange%20Specialized%20Killstreak%20Australium%20Stickybomb%20Launcher

Sales at :

48$

44$

43$

42$

44$

42$

Average of 43$ : 43 / 2.5 = 17 keys

Sale 3 :

Before : http://backpack.tf/profiles/76561198000417230?time=1428217200

After : http://backpack.tf/profiles/76561198000417230?time=1428303600

Sold for a Cloud 9 Carouser's Capotain : 13 keys

Mini on the capotain :

Before : http://backpack.tf/profiles/76561198130002084?time=1429254000

After : http://backpack.tf/profiles/76561198130002084?time=1429599600

Sold for a Dead Presidents Tam O' Shanter : 14 * 0.9 = 13 keys

Thus taking the range of 12 to 13 keys.

Supportive criticism welcome.

PS : thx to 3v1lcl0n3 for the help :)