3 month old price!

Sale 1: (invalid sale, used to price the Fedora)

Sold for Frostbite Fed-Fightin' Fedora + 9 keys

http://www.tf2outpost.com/trade/25754792

Backpack of buyer:

http://backpack.tf/profiles/76561198053134374?time=1431154800 (9th May)

http://backpack.tf/profiles/76561198053134374?time=1431241200 (10th May)

Backpack of seller:

http://backpack.tf/profiles/76561198002138145?time=1431154800 (9th May)

http://backpack.tf/profiles/76561198002138145?time=1431327600 (11th May)

Sale 2: (credits to back from waka!!!!! for the screenshot)

Sold for 50 keys + Specialised Australium Grenade Launcher (~19) + Australium Stickybomb Launcher (~15) + Australium Wrench (~23) + Australium Frontier Justice (~10)

50 + 19 + 15 + 23 + 10 = 117 keys (unfortunately, B/O caps it at 100 keys)

http://www.tf2outpost.com/trade/25927049

http://i.imgur.com/AbViINY.jpg

Backpack of buyer:

http://backpack.tf/profiles/76561198060237284?time=1431241200 (10th May)

http://backpack.tf/profiles/76561198060237284?time=1431327600 (11th May)

Backpack of seller:

http://backpack.tf/profiles/76561198053134374?time=1431241200 (10th May)

http://backpack.tf/profiles/76561198053134374?time=1431327600 (11th May)

Turns out this did not sell for $350 on SCM, that's for Sale 4.

Sale 3: (not certain on the sale, can be used as support-proof instead)

http://backpack.tf/profiles/76561197979473310?time=1432364400 (23rd May)

Sale 4:

Sold on SCM: http://steamcommunity.com/market/listings/440/Unusual%20Taunt%3A%20The%20Schadenfreude

http://www.tf2outpost.com/trade/25908284

Seller received: $304.36 = 121.744 (rounding to 122 keys) (keys were $2.50 on SCM at time of sale)

Buyer paid: $304.36*1.15 = $350.01 = 140.0056 (rounding to 140 keys) (keys were $2.50 on SCM at time of sale)

Sale 5: (invalid sale; outlier)

Sold for Specialised Australium Wrench (~24) + Specialised Australium Minigun (~22) = 46 keys

http://www.tf2outpost.com/trade/25803786

Backpack of buyer:

http://backpack.tf/profiles/76561198031371895?time=1430290800 (29th April)

http://backpack.tf/profiles/76561198031371895?time=1430377200 (30th April)

Backpack of seller:

http://backpack.tf/profiles/76561198173744193?time=1430118000 (27th April)

http://backpack.tf/profiles/76561198173744193?time=1430377200 (30th April)

Sale 6: (invalid sale)

Involved in a bulk deal for Hellfire Merc's Mohawk

http://www.tf2outpost.com/trade/25994165

Backpack of buyer:

http://backpack.tf/profiles/76561198004478413?time=1431673200 (15th May)

http://backpack.tf/profiles/76561198004478413?time=1432018800 (19th May)

Backpack of seller:

http://backpack.tf/profiles/76561198173925222?time=1431932400 (18th May)

http://backpack.tf/profiles/76561198173925222?time=1432018800 (19th May)

Notes:

http://www.tf2outpost.com/trade/25927049 - Offer of Darkblaze Pardner's Pompadour + 11 keys + Showstopper Deep Fried Desire = ~100 keys or so

For sale 3, if it did sell on SCM, the only sale between the 19th and 23rd of May was a $350 (~120 key) sale: http://i.imgur.com/qmGwFnF.png (can be used as support-proof)

As for sale 2, Australiums do not require that much overpay as opposed to majority of other items as they sell quite easily for pure. Even if the sale caps at 100 keys when it realistically sold for 117 keys, this indicates that it is evident that a Showstopper Schadenfreude can easily sell for over 100 keys.

Conclusion:

Valid sales at 100, 122 and 140 keys, along with a support-sale of 120 keys. Taking a final range of 100-140 keys.

Feel free to support/counter my suggestion!