First unusual suggestion, here goes.

Usable sales

Sold for 18 Pure:

http://backpack.tf/profiles/76561198004517334#!/compare/1490054400/1490140800

Auctioned off for Steaming Front Runner (15; mini below) + 1 Key mixed:

https://scrap.tf/auctions/VG85PW

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Mini: Steaming Front Runner (12 month old price)

Sold for 14 keys:

http://backpack.tf/profiles/76561198048312212#!/compare/1493337600/1493510400

Classifieds at 14-16 keys (Outlier at 20):

http://backpack.tf/classifieds?item=Front%20Runner&quality=5&tradable=1&craftable=1&australium=-1&particle=36&killstreak_tier=0

Sold in batch alongside Orbiting Fire Glengarry Bonnet (12) & 1 Key in items for Molten Mallard Glengarry Bonnet (29):

http://backpack.tf/profiles/76561198153298889#!/compare/1493337600/1493683200

Taking 15.

Thanks to raZ for guiding me through some doubts, I guess.