Sale #1:

Sold for Nuts Sultan's (outdated) + ~0.5 keys

http://backpack.tf/profiles/76561198004509501?time=1433401200 (June 4th)

http://backpack.tf/profiles/76561198004509501?time=1433648173 (June 7th)

Would be around equal value.

Sale #2:

Sold for Nuts Sultan's (again)

http://backpack.tf/profiles/76561198073537440?time=1433055600 (May 31st)

http://backpack.tf/profiles/76561198073537440?time=1433142000 (June 1st)

Would be around equal value.

Sale #3:

http://www.tf2outpost.com/trade/26089455

Sold for a Pro KS Strange Righteous Bison

http://backpack.tf/profiles/76561198055063451?time=1433228400 (June 2nd)

http://backpack.tf/profiles/76561198055063451?time=1433401200 (June 4th)

http://www.tf2outpost.com/trade/26084055

http://www.tf2outpost.com/trade/26041815 Bison seems to around 7 keys or less

Sale #4:

http://www.tf2outpost.com/trade/26138999

Quick-sold for 7 keys + 3 ref

http://i.imgur.com/iSp90i7.png

Sale #5:

http://www.tf2outpost.com/trade/26022946

Sold for a Specialized Aussie Tomislav (~9)

Buyer:

http://backpack.tf/profiles/76561198055063451?time=1431932400 (May 18th)

http://backpack.tf/profiles/76561198055063451?time=1432364400 (May 23rd)

Seller:

http://backpack.tf/profiles/76561198084892068?time=1432278000 (May 22nd)

http://backpack.tf/profiles/76561198084892068?time=1432364400 (May 23rd)

9 * 0.9 = ~8 keys

Most other sales are hard to trace. Seems to be around 8 keys. Many sellers are willing to take 7 keys to get rid of it. This really shouldn't be any higher than 9.

Support proof:

http://www.tf2outpost.com/trade/25572192 8 key B/O

http://www.tf2outpost.com/trade/26090325 Current seller at 8 keys, listed on market for $23.41 http://i.imgur.com/LHFfe5q.png

http://i.imgur.com/vjY9sqM.png Seller at 8 keys in classifieds

http://www.tf2outpost.com/trade/25928866 Unsold at 11 keys for 3 weeks

http://www.tf2outpost.com/trade/25570155 Was willing to take a Nuts Geisha (~8-9)

Just sold mine for 6 keys + ~2 keys in items

http://i.imgur.com/BB0eUdQ.png