Sale 1:

Sold for Circling Peace Sign Well-Rounded Rifleman (87)

No outpost

Seller: https://backpack.tf/profiles/76561198073472840#!/compare/1494115200/1494201600

Buyer: https://backpack.tf/profiles/76561198015330923#!/compare/1494115200/1494201600

X = 87

Sale 2:

Sold with Killstreak Aussie FaN (10) for Burning Festive Tree (Mini at 92 below) Below) + 3 keys

http://www.tf2outpost.com/trade/29265948 - B/O of 75

Seller: https://backpack.tf/profiles/76561198132960686#!/compare/1499644800/1500076800

Buyer: https://backpack.tf/profiles/76561198083063071#!/compare/1499990400/1500076800

X = 75 (Capped by B/O)

Sale 3:

Sold for Scorching Backbiter’s Billycock (73.5)

No outpost

Seller: https://backpack.tf/profiles/76561198015330923#!/compare/1494201600/1494374400

Buyer: https://backpack.tf/profiles/76561198070880686#!/compare/1494201600/1494374400

X = 74

Sale 4:

Sold for Fountain of Delight Burstchester (71) + cheap killstreak kits

No outpost

Seller: https://backpack.tf/profiles/76561198087172601#!/compare/1496707200/1496793600

Buyer: https://backpack.tf/profiles/76561198129552058#!/compare/1496707200/1496793600

X = 71

Sale 5:

Sold for Dead Presidents Brotherhood (58) + 25 keys

http://www.tf2outpost.com/trade/29219477 - B/O of 70

Seller: https://backpack.tf/profiles/76561198016530188#!/compare/1497139200/1497225600

Buyer: https://backpack.tf/profiles/76561198005273439#!/compare/1496793600/1497225600

X = 70 (Capped by B/O)

Sale 6:

Sold for HOUWAR (50 at the time) + 7 keys

No outpost

Seller: https://backpack.tf/profiles/76561198070880686#!/compare/1494633600/1494720000

Buyer: https://backpack.tf/profiles/76561198016530188#!/compare/1494633600/1494720000

X = 57

Sale 7:

Sold for Purple Energy Buckaroo’s + Dead Presidents Human Cannonball

Seller: https://backpack.tf/profiles/76561198313866674#!/compare/1495756800/1496016000

Buyer: https://backpack.tf/profiles/76561198184132174#!/compare/1495929600/1496016000

Too low to be looked into further.

Sale 8:

Bulk for Burning Greased Lightning

Seller: https://backpack.tf/profiles/76561198129552058#!/compare/1497916800/1498003200

Buyer: https://backpack.tf/profiles/76561198153402711#!/compare/1497916800/1498003200

Burning Tree Mini:

Sold for Terror-Watt Brotherhood of Arms (69) + Infernal Smoke Deep Fried Desire (17) + at least 10 keys worth of items

http://www.tf2outpost.com/trade/28901614 - B/O of 92

Seller: https://backpack.tf/profiles/76561198133443997#!/compare/1494201600/1494288000

Buyer: https://backpack.tf/profiles/76561198069326122#!/compare/1494288000/1494374400

X = 92 (Capped by B/O)

Sellers:

80 keys:

http://i.imgur.com/6uhxlye.png - 1 month

http://www.tf2outpost.com/trade/28425224

And another seller on marketplace for $155.

Sales at:

57

70

71

74

75

87

57 and 87 seem like outliers. Excluding 57 and 87.

Going with 70-75.

Big thanks to Happysedits for letting me take over :P