I may have accidentally worked on this suggestion before realising there was already one open. Here's what I got:

Duped Stormy 13th Salty Mini:

Sale 1:

Sold for Beams Allbrero (159) + Ghastly Ghosts Jr Vive La France (Mini at 185 below)

No outpost

Seller: http://backpack.tf/profiles/76561198066434918#!/compare/1491955200/1492041600

Buyer: http://backpack.tf/profiles/76561198136662317#!/compare/1491955200/1492041600

X = 339

Rounding to 340

Sale 2:

Sold for Circling Heart Casemaker (197.5) + Sulphurous Hive Minder (44)

No outpost

Seller: http://backpack.tf/profiles/76561197998161567#!/compare/1491782400/1491868800

Buyer: http://backpack.tf/profiles/76561198066434918#!/compare/1491696000/1491868800

X = 242

Rounding to 240

Sale 3:

Sold for Vivid Casemaker [in-date at 105-120, 2 month old seller at 99. Going with 100-120 (110) for this] + Duped Spellbound Nanobalaclava (Mini at 69 below) + Peace Sign Fortunate Son (Mini at 54 below)

http://www.tf2outpost.com/trade/28868533 - B/O of 310

Seller: http://backpack.tf/profiles/76561198090560650#!/compare/1491696000/1491782400

Buyer: http://backpack.tf/profiles/76561197998161567#!/compare/1491696000/1491782400

X = 223

Rounding to 225

Sellers:

299 keys:

http://www.tf2outpost.com/trade/28740777 - 4 months

http://backpack.tf/u/76561198017054389

300 keys:

http://i.imgur.com/HQr0x2R.png - 1 month

http://backpack.tf/u/76561198028853818

http://www.tf2outpost.com/trade/28905551

400?:

http://www.tf2outpost.com/trade/28718402 - 4 months

http://backpack.tf/u/76561198021228339

Offers:

http://www.tf2outpost.com/trade/28880660

http://backpack.tf/u/76561198044019620

340 is an outlier. 225-240 (232.5) for the Salty Dog.

Duped Spellbound Nanobalaclava Mini:

Sale 1:

Sold with <1 key in items for Anti-Freeze Caribbean Conqueror (69.5)

http://www.tf2outpost.com/trade/28849757 - No real B/O

Seller: http://backpack.tf/profiles/76561198129180692#!/compare/1490918400/1491004800

Buyer: http://backpack.tf/profiles/76561197998161567#!/compare/1490918400/1491004800

X = 69

69 for the nano

Circling Peace Sign Fortunate Son Mini:

http://backpack.tf/suggestion/59317e700e2cad5b6b43479e - (Credit to you)

Ghastly Ghosts Jr Vive La France Mini:

http://backpack.tf/suggestion/5931a4ca0e2cad6d432e72bc

I decided not to use the stash sale because it was pretty bulky, but that's up to you whether or not you wanna use it.