Full disclosure: I own one and I paid 10 buds pure for it.

Proof: http://imgur.com/Pr7dY1Y

When I was searching for a seller I noticed from other offers that the current BP.tf value is on the low side. If you think I'm doing this to increase the value of my backpack, the last comment on the 3rd trade shows that I was quite willing to pay 11 buds for this; this is my dream TF2 hat and I was willing to overpay to get it. Furthermore, this price change would mean my backpack would increase in value by less than 1%.

http://www.tf2outpost.com/trade/8127310

B/O: 11 buds

Notable offers:

Beams Tyrant's Helm - 9.1-10.2 buds

Purple Energy Cowl (3.9-4.7 buds) + Vintage Lid (5-6 buds) - 8.9-10.7 buds total

Ghosts Beak (7.2-7.7 buds) + Hearts Private Eye (3.1-3.7 buds) - 10.3-11.4 buds

He has an offer of a vintage parasite too, but I made that offer 2 months ago so I've discounted it.

http://www.tf2outpost.com/trade/10026660

No B/O

Notable Offers:

Green Energy Modest - 11.9-13.4 buds

Vintage Medal - 10 buds

10 buds pure (but not on the trade, claims he was added)

$385 - 11 buds

Cloudy Moon Lucky Shot - 8.5-10.1 buds

Vintage Parasite (not offered by me this time) - 8-9 buds

http://www.tf2outpost.com/trade/3418079

B/O: 11 buds

Notable offers (this thread has a LOT of offers so I'll name who made the offer so you can search for yourself):

Hotshotchicago- Stephanie's Hubs - 9 buds + 15 keys (9.5 buds at the time)

And a few other offers that have already been detailed above, other than that there are no offers considered by the seller in the last month.

As for a new suggested price:

I think that 10 buds is the logical choice for an upper value; it is the highest pure offer for which there is evidence and the high values of several unusual offers are around 10 buds.

The low end is more difficult to accurately ascertain however 9 buds is what I am going to suggest; all of the unusuals offered fall into this area, it's just a pity that there are no pure offers higher than 7 or lower than 10 buds to give a more accurate picture.

To sum up, 9-10 buds seems the best price; the GE Modest is an outlier and I don't really know how to fit it into my suggestion and so basically have to ignore it.

Let me know if you have any thoughts as I am fully open to the idea of re-suggesting if you think my evidence is flawed, but with several offers above the current price it definitely needs an update.