I'll do it...

Sale 1: (outlier)

Sold for 93 keys (~4.89) + *Overclocked Gridiron Guardian* (~1) + *Overclocked Broadband Bonnet* (~1) = 4.9 + 1 + 1 = 6.9 (rounding to 7)

http://www.tf2outpost.com/trade/19281619

http://imgur.com/a/8KPg9

Sale 2:

Sold for 2 buds (2) + Orbiting Fire Texas Tin-Gallon (1.35*0.9) + Smoking Master's Yellow Belt (1.8*0.9) = 2 + 1.215 + 1.62 = 4.835 (rounding to 5)

http://www.tf2outpost.com/trade/22109322

http://i.imgur.com/9gAW831.png

Sale 3:

Unsure what it really sold for, but has had an offer of Max's Head (3.3) + 12 keys (0.63) = 3.3 + 0.63 = 3.93 (rounding to 4)

B/O was also 4 buds. Seller is really inactive and trade is poorly bumped, but with an offer AND buyout of 4, valuing this sale at 4 buds.

http://www.tf2outpost.com/trade/15657564

Sale 4:

Relatively old sale, but still sold for 4 buds pure.

http://www.tf2outpost.com/trade/19747920

Sale 5: (obvious, extreme, crazy outlier!)

Sold for 10 buds pure

http://www.tf2outpost.com/trade/20457252

http://gyazo.com/d1d9d5bc391c840a463d6cb3fafd611c

Mini for Overclocked Gridiron Guardian: (credits to grimdercell for sales)

http://www.tf2outpost.com/trade/21247292 - 18-20 keys

http://www.tf2outpost.com/trade/21265344 - looking for 1.4 buds for 1 month...

"Heck, the gridiron isn't even worth 1.4 buds. It should be less than a bud seeing that the one in the first link was looking for 18-20 keys"

~ Taking price as 19 keys = 1 buds

Mini for Overclocked Broadband Bonnet:

http://i.imgur.com/6gxQMAN.png - sold for 1 buds (months old sale, but look at notes)

~ Taking price as 1 buds

Notes:

→ The mini-suggestions do not really matter because we all know that 'Sale 1' is evidently an outlier, seeing as how it adds to around ~7, whilst there aren't even any offers exceeding ~5.

→ 'Sale 3', as we all should have already known, is an obvious and outrageous outlier!

→ No consistent offers that have revolved around 7-10 buds for any of the trades. Most offers occurred within the 4-5 bud range, its safe to say that 'Sale 1' and 'Sale 5' are evident outliers.

→ Also, Roosebud (previous owner of 'Sale 5'), stated in one of the closed suggestions: "I'd just like to mention that when I had it up for trade the highest offer I received was 4.5 in pure and a couple of 4-5 in unusual offers."

→ 'Sale 4' is still arguably a valid sale even though it might be relatively old, as offers in other trades and overall recent sales have occurred within the 4-5 bud range.

Conclusion:

4-5 buds is the best and most suitable price range for this hat.

Feel free to support/counter my suggestion!