Sale 1:

Sold for 29 keys

http://www.tf2outpost.com/trade/28694832 - B/O of 30

Seller: http://backpack.tf/profiles/76561198043936328#!/compare/1483315200/1483401600

Buyer: http://backpack.tf/profiles/76561197989198267#!/compare/1483315200/1483401600

X = 29

Sale 2:

Sold for Burning Flames FR-0

http://www.tf2outpost.com/trade/28736380 - B/O of 26

Seller: http://backpack.tf/profiles/76561198050062763#!/compare/1485043200/1485129600

Buyer: http://backpack.tf/profiles/76561198121103199#!/compare/1485129600/1485216000

X = 26 (Capped by B/O)

Sale 3:

Quicksold for 19 keys

Seller: http://backpack.tf/profiles/76561198006855513#!/compare/1484784000/1484870400

Buyer: http://backpack.tf/profiles/76561198050062763#!/compare/1484697600/1484784000

X = 19

Sale 4:

Sold for Stormy Storm Helmet Without a Home + Spec .KS Aussie Black Box (14.5)

No outpost

Seller: http://backpack.tf/profiles/76561198042031300#!/compare/1487116800/1487203200

Buyer: http://backpack.tf/profiles/76561198300711587#!/compare/1487030400/1487203200

Considering the seller is re-selling the Helmet at 14, and the buyers at 11, it should be safe to value the Helmet anywhere between 12-14. Any of these values will allow this sale to fit in the range.

Sellers:

26 keys:

http://i.imgur.com/KowMU8s.png - 5 days

http://backpack.tf/u/76561198344933095

27 keys:

http://www.tf2outpost.com/trade/28719411 - 1 month

http://backpack.tf/profiles/76561198051515564 (probably on scm, if not traded away)

Sales at:

19

26

29

19 quicksold, excluding 19.

Going with 26-29.