Did some digging here and got mixed results:

Three were up for trade, currently just one.

http://www.tf2outpost.com/trade/5815072 traded it for a beams fuka + g.fetti buto = ~6.8 pure

http://www.tf2outpost.com/trade/5839734 + http://www.tf2outpost.com/trade/6178341 = http://www.tf2outpost.com/trade/6483443 he was brokering btw: http://www.tf2outpost.com/trade/6224296 - the secret ywn isn't priced at, I would say ~15 buds - 2buds in items = ~13 buds --> lucky one

http://www.tf2outpost.com/trade/5699051 - bought with 5 pure, quicksell price

http://www.tf2outpost.com/trade/5838416 - sold for scorching swagmans = ~6.3 pure

http://www.tf2outpost.com/trade/6125414 - traded for cloudy trophy belt + sweets (~6 pure), the trophy belt was his dream hat, so no unusual overpay

http://www.tf2outpost.com/item/440/1273422956 - traded for a misty skull drill, he offered that on the current trade as well (~6.2 pure)

http://www.tf2outpost.com/trade/7478848 - brokering? (he is in his friend list)

http://www.tf2outpost.com/trade/7826693 - brokering - sold

http://www.tf2outpost.com/backpack/108994 --> http://www.tf2outpost.com/backpack/203981 - Traded for a knifestorm billycock + 3.4 buds = ~8.4 pure

http://www.tf2outpost.com/trade/6034096 - current trade - someone offered 9 pure but bought something else.

So yeah we have trades from 5 - 13 buds. The 5 buds and the 13 buds trades are clearly outliers. Some are traded from 6-7 buds but back then prices of unusuals were higher, so let's say 7-8 ( http://backpack.tf/vote/id/509e0bd1ba2536c016000004 ). One recent trade valued at ~8.4 buds and one offer of 9 buds, but he bought something else, because they didn't respond. As on the most halloween unusuals, very few offers --> still a large range.

Conclusion: I suggest 7-9 buds because at 7 the most old trades took place. And 9 because of the 1 recent trade and the 1 recent offer.

Took me a full hour. -.-