Sale 1:

Sold for 18 keys

http://www.tf2outpost.com/trade/28841223 - B/O of 18

Seller: http://backpack.tf/profiles/76561198002757046#!/compare/1490745600/1490832000

Buyer: http://backpack.tf/profiles/76561198061726446#!/compare/1490832000/1491609600

X = 18

Sale 2:

Sold for 17 keys + ~1 key in metal/items in ~2-3 days

No outpost

Seller: http://backpack.tf/profiles/76561198269178506#!/compare/1492214400/1492300800

Buyer: http://backpack.tf/profiles/76561198081413086#!/compare/1492214400/1492646400

X = 18

Sale 3:

Sold with 2 keys for Miami Baker Boy?

No outpost

Seller: http://backpack.tf/profiles/76561198092487977#!/compare/1491868800/1492041600

Buyer: http://backpack.tf/profiles/76561198269178506#!/compare/1491955200/1492041600

Not entirely convinced that this sale is correct, but it can probably be used to update the Baker boy anyways. If it were to be used here, it could create an unnecessarily large range.

Sale 4:

Bulk for something

Seller: http://backpack.tf/profiles/76561198104098977#!/compare/1493078400/1493164800

Buyer: http://backpack.tf/profiles/76561198056086416#!/compare/1493078400/1493164800

Sale 5:

Bulk for several things

Seller: http://backpack.tf/profiles/76561198056086416#!/compare/1493078400/1493164800

Buyer: http://backpack.tf/profiles/76561198075532147#!/compare/1492819200/1493164800

Sales at:

18 (2x)

No current sellers.

One of the sales at 18 happened rather quickly, however, the new owner never re-listed for sale, so it should be fine to keep 18, as the owner appears to be keeping the hat. That, and the other sale at 18 took a little more than 3 weeks.

Going with 18 flat.