3 on OP, 2 B/Os are set at 4 buds which means 4.3 as a high end is pretty much outdated.

http://www.tf2outpost.com/trade/8595788 - Already have a guy willing to buy it for 4 (gathering), some people offered some unusuals worth around 3.2 (Steaming Soldier's Slope Scopers, Smoking Brown Bomber)

http://www.tf2outpost.com/trade/8383363 - At the bottom, he says he wants to sell it for 4. 3 buds + 6 keys are highest offer so far, which is around 3.2 buds.

http://www.tf2outpost.com/trade/8633896 - Very high B/O, saying he is not gonna trade for 4 buds but... he didn't get any pure offers.

In conclusion, many offered unusuals around 3.2 buds. Two people wanted to sell this hat for 4 pure and one of them got a buyer who wants to buy it in a week. Based on these, 3.2 ~ 4 buds seems good