Sale 1:

Sold for Strange Aces High Elf Esteem (no recent sales, going with non-strange price of 10) + Steaming Ze Goggles (Mini at 12 below)

http://www.tf2outpost.com/trade/28824844 - B/O of 20

Seller: http://backpack.tf/profiles/76561198107520045#!/compare/1490400000/1490486400

Buyer: http://backpack.tf/profiles/76561198135942517#!/compare/1490400000/1490486400

X = 20 (Capped by B/O)

Sale 2:

Sold for 19 keys + 2 scrap

No outpost

Seller: http://backpack.tf/profiles/76561198099306504#!/compare/1491868800/1492560000

Buyer: http://backpack.tf/profiles/76561198326403130#!/compare/1492819200/1493596800

X = 19

Sale 3:

Sold for 18 keys + ~1 key in items in ~1 day

http://www.tf2outpost.com/trade/28893700 - B/O of 19.5

Seller: http://backpack.tf/profiles/76561198235889590#!/compare/1493078400/1493164800

Buyer: http://backpack.tf/profiles/76561198091930188#!/compare/1493078400/1493164800

X = 19

Sale 4:

Quicksold for 17 keys

Seller: http://backpack.tf/profiles/76561198003926663#!/compare/1492992000/1493078400

Buyer: http://backpack.tf/profiles/76561198235889590#!/compare/1492992000/1493078400

X = 17

Sale 5:

Quicksold for 16 keys

Seller: http://backpack.tf/profiles/76561198095862827#!/compare/1488326400/1488412800

Buyer: http://backpack.tf/profiles/76561198107520045#!/compare/1488326400/1488412800

X = 16

Sale 6:

Sold for Orbiting Fire Reggae + 1 key

Seller: http://backpack.tf/profiles/76561198288714795#!/compare/1487894400/1487980800

Buyer: http://backpack.tf/profiles/76561198130579834#!/compare/1487894400/1487980800

Numerous sellers for cheaper on the Reggae, would be best not to use its current price. May be better to update the Reggae with this sale, even.

Sale 7:

Sold with 14 keys + Stickybomb launcher skin for Dead Presidents Rifleman

Seller: http://backpack.tf/profiles/76561198123090943#!/compare/1489017600/1489104000

Buyer: http://backpack.tf/profiles/76561198069490363#!/compare/1488672000/1489190400

Should be used on the Rifle

Sale 8:

Bulk for Green Energy Metal Drill

Seller: http://backpack.tf/profiles/76561198324135359#!/compare/1488240000/1488412800

Buyer: http://backpack.tf/profiles/76561198095862827#!/compare/1488326400/1488412800

Sale 9:

Sold for Cloud 9 Glasgow (19) + Schadenfreude (1)

No outpost

Seller: http://backpack.tf/profiles/76561198162277492#!/compare/1492732800/1492819200

Buyer: http://backpack.tf/profiles/76561198167488923#!/compare/1492819200/1492905600

Was used to update the Glasgow.

Sale 10:

Sold for Searing Plasma Handyman’s Handle + Killstreak Aussie SMG + cheap taunt

Seller: http://backpack.tf/profiles/76561198130579834#!/compare/1487980800/1488067200

Buyer: http://backpack.tf/profiles/76561198324135359#!/compare/1488067200/1488153600

Was used on the Handle.

Steaming Goggles Mini:

Sold 4 times for $25 on marketplace.tf

https://marketplace.tf/items/177;5;u36

25/2.1 = 11.9, rounding to 12.

X = 12 (x4)

Sellers:

20 keys:

http://i.imgur.com/Dfc7H5k.png - 12 days

http://backpack.tf/u/76561198129088942

http://www.tf2outpost.com/trade/28908786

http://i.imgur.com/7YrqPZ9.png - 7 days

http://backpack.tf/u/76561198311911589

Offers:

http://www.tf2outpost.com/trade/28564103

http://backpack.tf/u/76561198079275897

Sales at:

16

17

19 (2x)

20

Ignoring how quickly sale 3 sold, looks like the seller lucked out, if anything. Sales and sellers point to around that price range.

16 and 17 quicksold. Excluding 16 and 17.

Going with 19-20.