7 month old price!

Sale 1:

Sold for 42 keys

http://www.tf2outpost.com/trade/27961742

http://backpack.tf/profiles/76561198031371895/#!/compare/1458716400/1458802800

Sale 2: (outlier)

Sold for Professional Australium Grenade Launcher = ~28 keys

http://www.tf2outpost.com/trade/27821699

http://backpack.tf/profiles/76561198144034994/#!/compare/1458111600/1458198000

Sale 3: (unusable, sale would be too low)

Sold with Morning Glory Safe'n'Sound for Unusual Grenade Launcher

http://www.tf2outpost.com/user/886036 | http://www.tf2outpost.com/trade/27946948

http://backpack.tf/profiles/76561197968530016/#!/compare/1458025200/1458111600

Notes:

http://www.tf2outpost.com/trade/27821699 - C/O of 34 keys

Conclusion:

One valid sale at 42 keys. Taking a final flat price of 42 keys.

Feel free to support/counter my suggestion!