First pricing with decimal points for the latest recent suggestion. Gonna update the price + slightly narrow the range.

Sale 1. (13-10-2016)

Sold for a Bills Hat (worth 2 Keys at the time of sale) + 12 Keys = 14 Keys

http://backpack.tf/profiles/76561198153939217#!/compare/1476230400/1476316800

http://www.tf2outpost.com/trade/28530481

Sale 2. (18-10-2016)

Sold for a Green Confetti Prussian Pickelhaube + 1 Key

X = 18 + 1

X = 19 Keys

http://backpack.tf/profiles/76561198153939217#!/compare/1476662400/1476748800

No outpost.

Pickelhaube mini.

http://backpack.tf/suggestion/5820da6383de6b5d4e0a26c5

Sales at 14 and 19 Keys. Taking range as 14-19 Keys.