requested; 1 of 1 in existence and sold to a collector!

Sale 1: (credits to Reg for providing screenshots of the trade)

Sold for 560 keys + Pro Australium Grenade Launcher* (28) + Australium Medi Gun (25) + Pro Australium Minigun* (30) + Pro Australium Rocket Launcher* (64) = 560 + 28 + 25 + 30 + 64 = 707 keys (rounding to 710 keys)

http://www.tf2outpost.com/trade/25722574

http://gyazo.com/9544124d317877d308ca1e76fdf7e9db | http://gyazo.com/38593ea16b63b0d3d6b8049471a0df03

http://backpack.tf/profiles/76561198065493736?time=1430463600 - before

http://backpack.tf/profiles/76561198065493736?time=1430550000 - after

Mini-suggestion for Pro Australium Grenade Launcher*: (after tax)

$69.57 | $73.91 | $69.58 | $65.78 | $65.02

Average value of $68.77 = ~28-29 keys

Mini-suggestion for Pro Australium Minigun*: (after tax)

$69.57 | $83.37 | $71.30 | $69.57 | $74.92

Average value of $73.75 = ~30-31 keys

Mini-suggestion for Pro Australium Rocket Launcher*: (after tax)

$156.17 | $156.53 | $156.94 | $147.83 | $160.00

Average value of $155.49 = 64~65 keys

Notes:

Hat in question: http://backpack.tf/item/3543296551

http://www.tf2outpost.com/trade/25722574 - Had a C/O of 560 keys + Professional Australium Medi Gun = ~605 keys

Conclusion:

One very recent sale at ~710 keys. Sold to a collector who doesn't plan to sell it any time soon; taking a final value of 710 keys.

Feel free to support/counter my suggestion!