Sale 1:

Sold for Kill-a-Watt Baker Boy (17)

No outpost

Seller: https://backpack.tf/profiles/76561198231040628#!/compare/1532649600/1532736000

Buyer: https://backpack.tf/profiles/76561198064526459#!/compare/1528761600/1532736000

https://backpack.tf/item/5129395752

X = 17

Sale 2:

Sold for $30 on marketplace.tf

https://marketplace.tf/items/30334;5;u7

https://backpack.tf/item/6794810791

http://www.tf2outpost.com/trade/29712378 - B/O of 18

http://manic.tf/keyprice/?at=2018-07-23 - $30 / $1.95 = 15.38 keys

X = 15

Sale 3:

Bought from scrap.tf for 12 keys + ~1 key in metal

Seller: https://backpack.tf/profiles/76561198135388328#!/compare/1532563200/1532649600

Buyer: https://backpack.tf/profiles/76561198231040628#!/compare/1532563200/1532649600

https://backpack.tf/item/5129395752

X = 13

Sale 4:

Sold for 13 keys

Seller: https://backpack.tf/profiles/76561198096237015#!/compare/1530230400/1530316800

Buyer: https://backpack.tf/profiles/76561198164351921#!/compare/1530230400/1530316800

https://backpack.tf/item/6794810791

X = 13

Sale 5:

Bulk for Bubbling Bonk Boy

Seller: https://backpack.tf/profiles/76561198045713630#!/compare/1528502400/1529020800

Buyer: https://backpack.tf/profiles/76561198050436077#!/compare/1528416000/1528502400

https://backpack.tf/item/6794810791

Sale 6:

Untraceable

Seller: https://backpack.tf/profiles/76561198050436077#!/compare/1528502400/1528588800

Buyer: https://backpack.tf/profiles/76561198164549423#!/compare/1527638400/1528588800

https://backpack.tf/item/6794810791

Sale 7:

Sold with ~1 key in items for Orbiting Fire Bubble Pipe

Seller: https://backpack.tf/profiles/76561198164549423#!/compare/1528588800/1528675200

Buyer: https://backpack.tf/profiles/76561198108367803#!/compare/1528156800/1528675200

https://backpack.tf/item/6794810791

Better to use on the Bubble Pipe.

Sale 8:

Sold with keys for Searing Head Hedge

Seller: https://backpack.tf/profiles/76561198108367803#!/compare/1528934400/1529020800

Buyer: https://backpack.tf/profiles/76561198101899047#!/compare/1528848000/1529020800

https://backpack.tf/item/6794810791

Better off being used on the Hedge.

Sale 9:

Bulk

Seller: https://backpack.tf/profiles/76561198101899047#!/compare/1529971200/1530316800

Buyer: https://backpack.tf/profiles/76561198096237015#!/compare/1530144000/1530230400

https://backpack.tf/item/6794810791

Sale 10:

Bulk? for Smoking Bonk Boy

Seller: https://backpack.tf/profiles/76561198164351921#!/compare/1530230400/1530316800

Buyer: https://backpack.tf/profiles/76561198218628708#!/compare/1530230400/1530316800

https://backpack.tf/item/6794810791

Sale 11:

Untraceable, probably bulk

Seller: https://backpack.tf/profiles/76561198218628708#!/compare/1530230400/1530316800

Buyer: https://backpack.tf/profiles/76561198070266530#!/compare/1530230400/1530316800

https://backpack.tf/item/6794810791

Sale 12:

Bulk for Chiroptera Venenata Bombing Run

Seller: https://backpack.tf/profiles/76561198070266530#!/compare/1530230400/1530316800

Buyer: https://backpack.tf/profiles/76561198122604075#!/compare/1530230400/1530316800

https://backpack.tf/item/6794810791

Sale 13:

Untraceable, sold to a bot

Seller: https://backpack.tf/profiles/76561198218857377#!/compare/1532390400/1532476800

Buyer: https://backpack.tf/profiles/76561198316961222#!/compare/1532304000/1532390400

https://backpack.tf/item/6794810791

Sale 14:

Bulk for Chiroptera Venenata Big Elfin Deal

Seller: https://backpack.tf/profiles/76561198133040286#!/compare/1531785600/1532044800

Buyer: https://backpack.tf/profiles/76561198035701234#!/compare/1531872000/1532044800

https://backpack.tf/item/5129395752

Sale 15:

Untraceable, sold to scrap.tf

https://backpack.tf/profiles/76561198035701234#!/compare/1531872000/1532044800

https://backpack.tf/item/5129395752

Sellers:

https://gyazo.com/cd53970b1f152bcebf3c467314ecc62f

https://backpack.tf/item/3902413843 - 19 keys

https://backpack.tf/item/4021809325 - 19 keys

Sales at:

13 (2x)

15

17

Going with 13-17.