Sale 1:

http://backpack.tf/profiles/76561198159933043#!/compare/1495238400/1495324800

Sold for a Misty Skull Backbiter's Billycock (~64)

http://www.tf2outpost.com/trade/29132317 - B/O 65

Rounding up to 65

Sale 2:

http://backpack.tf/profiles/76561198043976007#!/compare/1493942400/1494288000

Sold with 2 keys for a Holy Grail Taunt: Second Rate Sorcery (~78)

=76

http://www.tf2outpost.com/trade/28841023 - B/O 70

Sale 3:

http://backpack.tf/profiles/76561198043976007#!/compare/1489968000/1490054400

Sold for a Duped Circling Heart Big Country?

Outlier anyway.

Sale 4:

http://backpack.tf/profiles/76561198065110530#!/compare/1496016000/1496102400

Sold with a C9 Fruit shoot (18) for a Blizzard KE(68)

= 50

Happened after this suggestion was posted. A bit bulky. Excluding for now.

Sales:

65

70

50

Going with 65 - 70