Sale 1:

https://backpack.tf/profiles/76561197982879578#!/compare/1548115200/1548201600

https://backpack.tf/profiles/76561198170686275#!/compare/1548115200/1548201600

= Strange Festivized Professional Killstreak Kritzkrieg (26.98 keys) + Strange Professional Killstreak Quick-Fix (6.34 keys) + Strange Festivized Professional Killstreak Loose Cannon (5.45 keys)

= 38.77

~ 39 keys (duped)

Sale 2:

https://backpack.tf/profiles/76561198170686275#!/compare/1549324800/1549584000

https://backpack.tf/profiles/76561198303886984#!/compare/1549411200/1549497600

= Green Energy Buckaroos Hat (28.5 keys)

~ 29 keys

Sale 3:

https://marketplace.tf/items/338;5;u64

= $63.99 / $1.75 (Jan 8th)

= 36.56...

~ 37 keys

Summary: 29, 37, 39

Conclusion: pricing at 37 keys as per recommended by TF2Scourge. Excluding Sale 2 due to being below buy orders.

Yes, I am aware of the 35 key seller on classifieds and I will probably update this suggestion at a later date if he sells it anytime soon (or just close this all together).