Before I begin, I know this isn't all the proof there is, but I think there is enough here to convince you of my range

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http://www.tf2outpost.com/trade/19851691 - QS for 55 keys (3.2 buds)

http://www.tf2outpost.com/trade/19795785 - added Searing Tree for MN Tossle http://www.tf2outpost.com/trade/19894859

~ 3.8 buds

http://www.tf2outpost.com/trade/19709810 - Stormy Modest (slightly outdated) + 10 keys in sweets

~ 4 buds (offered)

http://www.tf2outpost.com/trade/19694859 - appears to have traded for those

~ 3.2 buds (outlier)

http://www.tf2outpost.com/trade/19596876 - Lantern Private Eye http://www.tf2outpost.com/trade/19598176

~ 3.7 buds (outlier, went rather quickly)

http://www.tf2outpost.com/trade/19544034 - Steaming TC (slightly outdated) + Mirror http://www.tf2outpost.com/trade/19571770

~ 4.4 buds

http://www.tf2outpost.com/trade/19529904 - KaW HWNN + 1 bud

~ 4.4 buds

http://www.tf2outpost.com/trade/19437499 - Offered on a duped Scorching Tricone

~ 4.5 buds (B/O)

http://www.tf2outpost.com/trade/19725542 - KaW Tree + TW Guad + 10 keys

~ 5.2 buds (obvious outlier)

http://www.tf2outpost.com/trade/19660907 - KaW Tree + TW Guad + 9 keys(LOL)

~ 5.1 buds

http://www.tf2outpost.com/trade/19667878 - 4 buds

http://www.tf2outpost.com/trade/19265725 - Roboactive HH-Lamp (BUT had an interested buyer for 4 buds)

http://www.tf2outpost.com/trade/19537521 - DBD HWNN (unpriced)

http://www.tf2outpost.com/trade/19592341 - Secret Ketche

Sales: 3.2, 3.2, 3.7, 3.8, 4, 4, 4.4, 4.4, 4.5, 5.1, 5.2

I think a nice 4-4.5 would be good enough

Feedback and additional proof is appreciated.