Sale 1:

Sold for 25 keys (25/15.25) = 1.64 (B/O was 1.5 before editting notes, so valuing at 1.5)

http://www.tf2outpost.com/trade/23783895

http://backpack.tf/profiles/76561198038541714?time=1416470400 → http://backpack.tf/profiles/76561198038541714?time=1416556800

Sale 2: (invalid sale, unpriced hat)

Sold with ~2 buds in mixed for Frostbite Jumper's Jeepcap

http://www.tf2outpost.com/trade/24064018

http://backpack.tf/profiles/76561198119680565?time=1418457600 → http://backpack.tf/profiles/76561198046487200?time=1418457600

Sale 3: (invalid sale, outdated hat + unpriced hat)

Sold with Dead Presidents Dread Riding Hood for Darkblaze Head Warmer

http://backpack.tf/profiles/76561198046487200?time=1417852800 → http://backpack.tf/profiles/76561198036743959?time=1417865235

Sale 4: (invalid sale, outlier)

Sold for Lucky No. 42 + Genuine Merc's Pride Scarf + 5 Vintage Cosmetics = ~1.1 buds

http://www.tf2outpost.com/trade/23041996

http://backpack.tf/profiles/76561198069140011?time=1413131467 → http://backpack.tf/profiles/76561198069140011?time=1413270000

Sale 5:

Sold for 1 buds + 9 keys + Strange Specialised Quick Fix = >1.5 buds (B/O was 1.5 buds, so valuing at 1.5)

http://www.tf2outpost.com/trade/23695868

Notes:

For valuing the buds, I'm using the price at the time of sale.

http://www.tf2outpost.com/trade/23041996 - B/O 1.5 buds

http://www.tf2outpost.com/trade/23695868 - B/O 1.5 buds

Conclusion:

Sales at 1.1, 1.5, 1.5 and B/Os at 1.5, 1.5. Valuing final price at 1.5 buds.

Feel free to support/counter my suggestion!