I think the last suggestion was innaccurate with the higher end of the scale.

In the proof shown below i will show you links that get offers that vary between 16 and 24 keys. Some of these offers are in items

16-17 Key offers

http://www.tf2outpost.com/trade/10040689 Offer of Bacon Grease declined by owner.

17 Keys

http://www.tf2outpost.com/trade/9934851 Offer of 17 pure, but retracted after made c/o by owner.

http://www.tf2outpost.com/trade/9649214 Got offered 17 pure

http://www.tf2outpost.com/trade/10144116 Got offered 17 pure on the first day of the trade being up

19 Keys

http://i.imgur.com/NTt2D9z.jpg Screenshot of one selling for 19 keys just over a week ago

Misc.

http://www.tf2outpost.com/trade/9649214 Offer of Stormy Storm Exquisite Rack, if owner adds

http://www.tf2outpost.com/trade/9934851 Offered a 1:1 trade with a steaming salty dog (valued at 22-24 keys)

I have shown you every relevant trade on outpost that i could find and others i find will be added below.

http://www.tf2outpost.com/trade/8520714 Ended up selling for 18 keys

http://www.tf2outpost.com/trade/8608699 This guy got offered 2 painted bills + 5 ref and 20 keys by a different person. ended up getting the 20 keys

I've also got evidence from recent suggestions that people do believe in this price

http://backpack.tf/vote/id/516b65d9ba25369a3100000e