Credits to brendan [HAXMAS] for the suggestion!

Sale 1:

Sold for 1 buds + 10 keys (10/15.25) = 1 + 0.66 = 1.66 (rounding to 1.7)

http://www.tf2outpost.com/trade/23838453

http://i.imgur.com/rPsl29s.png

Sale 2:

Sold for 2 buds

http://www.tf2outpost.com/trade/23885742

http://i.imgur.com/94iqqZq.png

Sale 3:

Sold for 1 buds + 5 keys (5/12.5) = 1 + 0.4 = 1.4

http://www.tf2outpost.com/trade/24088857

http://backpack.tf/profiles/76561198041350434?time=1418803200 → http://backpack.tf/profiles/76561198041350434?time=1418889600

Sale 4: (invalid sale)

Sold with Orbiting Planets Bonk Boy for ★ Bayonet

http://www.tf2outpost.com/trade/23584751

http://www.tf2outpost.com/item/730,920765550,500,3

Sale 5:

Sold for 1 buds + 15 keys + 9 ref = 1 + (~15.8/15.5) = 1 + 1.01 = 2.01 (rounding to 2)

http://www.tf2outpost.com/trade/23305421

http://backpack.tf/profiles/76561198035884807?time=1414663669

Notes:

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

Conclusion:

Sales at 1.4, 1.7, 2, 2. Valuing final range at 1.4-2 buds.

http://www.tf2outpost.com/trade/24088857 - B/O of 1.5 buds

http://www.tf2outpost.com/trade/24198007 - B/O of 2 buds

Feel free to support/counter my suggestion!