"Tempest"

Sold for Smoking Plumber's ~10 Keys

http://backpack.tf/profiles/76561198151648479?time=1438239600

http://backpack.tf/profiles/76561198151648479?time=1438326000

Sold for TW Raincatcher ~15 Keys

http://backpack.tf/profiles/76561198149404767?time=1438412400

http://backpack.tf/profiles/76561198149404767?time=1438498800

Sold for TW Metal Modest (27 Keys) w/ 4 Keys + Sweets (~1 Keys) ~22 Keys

http://backpack.tf/profiles/76561198076107441?time=1441436400

http://backpack.tf/profiles/76561198076107441?time=1441695600

http://www.mx7.com/view2/yAzwKaJjSzgJI9Qw

http://www.mx7.com/view2/yAzxiyFtnW7AXVKP

Sold for Planets Razor (~18 Keys) + Sweets (~1 Key) ~19 Keys

http://backpack.tf/profiles/76561198127332051?time=1439794800

http://backpack.tf/profiles/76561198127332051?time=1440399600

Sales at 10, 15, 19, 22 Keys.

The sale at 10 is definitely an outlier. The sale at 15 might be one, but since it's 2 months ago, it's hard to decide if the value at that time was 15.

Using 19-22 Keys as suggested by Polar.

Re-suggesting: http://backpack.tf/vote/id/55f043a2b98d88e6708b4645