Updating this year old price :

Sale 1 :

Before : http://backpack.tf/profiles/76561198062871196?time=1432796400

After : http://backpack.tf/profiles/76561198062871196?time=1432882800

Sold as well as a purple energy spartan for a : buning pith helmet (87 keys) - purple energy spartan ( 49 keys ) = 35 keys with overpay applied.

Sale 2 :

Before : http://backpack.tf/profiles/76561198051956029?time=1432018800

After : http://backpack.tf/profiles/76561198051956029?time=1432105200

Sold for a spec ks aussie sniper : 90$ / 2.5 = 36 keys

http://steamcommunity.com/market/listings/440/Strange%20Specialized%20Killstreak%20Australium%20Sniper%20Rifle

Sale 3 :

Before : http://backpack.tf/profiles/76561198052803733?time=1427785200

After : http://backpack.tf/profiles/76561198052803733?time=1427871600

Sold for a purple energy worst nightmare but a 13th hour pencil pusher was added : 95 - 72 = 23 keys (outlier)

Mini of the nighmare :

Before : http://backpack.tf/profiles/76561198054156336?time=1428390000

After : http://backpack.tf/profiles/76561198054156336?time=1428735600

Sold for an aussie sniper rifle ( 34 keys ) + pro ks aussie smg ( 35$ / 2.5 = 14 keys ) + st pro ks kukri ( 7$ / 2.5 = 3 keys ) + frosbite crocleather slouch ( 44 keys ) = 95 keys

SMG : http://steamcommunity.com/market/listings/440/Strange%20Professional%20Killstreak%20Australium%20SMG

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

Mini on the pencil pusher : No recent sale on this hat. Taking its normal price of 72 keys.

Thus taking a range of 35 to 36 keys.