Sale 1:

Sold for 15 keys + ~4 keys in items

http://www.tf2outpost.com/trade/28904648 - B/O of 18

Seller: http://backpack.tf/profiles/76561198150783829#!/compare/1494201600/1494288000

Buyer: http://backpack.tf/profiles/76561198060820651#!/compare/1494201600/1494288000

X = 18 (Capped by B/O)

Sale 2:

Sold for 15 keys

http://www.tf2outpost.com/trade/28836550 - B/O of 15

Seller: http://backpack.tf/profiles/76561198005032783#!/compare/1491868800/1491955200

Buyer: http://backpack.tf/profiles/76561198096260332#!/compare/1491955200/1492041600

X = 15

Sale 3:

Bulk for keys

Seller: http://backpack.tf/profiles/76561198096260332#!/compare/1493424000/1493510400

Buyer: http://backpack.tf/profiles/76561198150783829#!/compare/1493424000/1493510400

Sale 4:

Sold with several keys worth of items for Slumber Metal Drill

Seller: http://backpack.tf/profiles/76561198060820651#!/compare/1494288000/1494460800

Buyer: http://backpack.tf/profiles/76561198124922135#!/compare/1494288000/1494374400

Can be used on the Drill.

Sellers:

15 keys:

http://i.imgur.com/zgzNWQd.png - 8 days

http://backpack.tf/u/76561198108148076

25 keys:

http://i.imgur.com/UlhMeRG.png - listed for 28 here

http://backpack.tf/u/76561198124922135

http://www.tf2outpost.com/trade/29172795

Sales at:

15

18

Going with 15-18.