This was difficult to decide on a range for, hopefully I got it about right.

http://www.tf2outpost.com/trade/24223935 - Sold for Burning Flames Glengarry Bonnet (4.5 buds after overpay)

http://www.tf2outpost.com/trade/24084401 - Sold for 63 keys pure ( http://backpack.tf/profiles/76561198046453101?time=1418803200 --> http://backpack.tf/profiles/76561198046453101?time=1418889600 ) buds were 12.5 keys at the time, so 5.04 buds, rounding down to 5 buds

http://www.tf2outpost.com/trade/23798106 - sold for 6.2 buds pure, but B/O was 6.

http://www.tf2outpost.com/trade/23776967 --> http://www.tf2outpost.com/trade/23874987 - Sold alongside 3 buds for Scorching Tree (7.2 buds after overpay), makes sunbeams tree 4.2 buds.

http://www.tf2outpost.com/trade/23568699 - Sold for GE Tree (4.2 buds after overpay) + 2 buds pure – makes sunbeams tree 6.2 buds

BF Glengarry Bonnet mini:

http://www.tf2outpost.com/item/440,3349789436,100,5 + http://www.tf2outpost.com/item/440,3421041300,143,6 --> http://www.tf2outpost.com/item/440,3427671340,465,5 Glengarry + 1 bud sold for Sunbeams Conjurer’s Cowl. Valuing Cowl with this suggestion: http://backpack.tf/vote/id/54a81272b98d88e86f8b4633 makes the Glengarry 5.04 buds after overpay, rounding to 5 buds

Summary of sales: 4.2 buds (m), 4.5 buds(u), 5 buds(p), 6 buds(p), 6.2 buds(m)

Current market:

http://www.tf2outpost.com/trade/24349760 – offers in range of ~5 buds unusual declined

http://www.tf2outpost.com/trade/22675593 - offers in range of 5-5.5 buds pure or unusual

Seems to be difficult to buy this for around 4.2 or 4.5, marking those two as outliers, making the range 5-6.2. Special thanks go to ♥Prof Sugarcube™♥, Jacobmeister and ShadowMan for giving me advice on choosing the range of this suggestion. If there is anything else I missed, feel free to tell me where I went wrong.