https://gyazo.com/2739c57f5a9fbd1417b7c5dbfa666912 - scrap selling at 16.5 keys

https://gyazo.com/df89f1cc19748c12f32306e0d23f9366 - classifieds at 19, 20, 22 keys (and mp.tf listing at 20ish)

Other sales:

https://backpack.tf/profiles/76561198336633071#!/compare/1532476800/1532649600

https://backpack.tf/profiles/76561198055622215#!/compare/1532563200/1532649600

http://www.tf2outpost.com/user/76561198336633071 - no B/O

Appears to have sold for a Starstorm Slumber Bot Dogger (19).

https://backpack.tf/profiles/76561198146640595#!/compare/1529020800/1529366400

https://backpack.tf/profiles/76561198165055074#!/compare/1529280000/1529366400

Bulk.

https://backpack.tf/profiles/76561198027260891#!/compare/1530144000/1531353600

https://backpack.tf/profiles/76561198214513491#!/compare/1530403200/1530576000

19 keys.

https://backpack.tf/profiles/76561198214513491#!/compare/1529971200/1530230400

https://backpack.tf/profiles/76561197961643548#!/compare/1529971200/1530057600

Sold for 21 keys.

I'm inclined to say that 21 is high as well here; looking at the current unsolds and the fact that the person who paid 21 resold it for 19 within 4 days.

The scrap.tf listing at 17 keys is 2 weeks old and there's have been 2 scrap transactions before (dumping and bought off scrap) -> https://backpack.tf/item/6968265928 , along with the fact that it remained unsold at 18 keys ( http://www.tf2outpost.com/trade/29705676 ) supports including 17 here.

Resuggest at 17-19 keys.