Two of these are currently on the market on Outpost, so there's a somewhat limited body of evidence from which to draw values. One of them has a 10-bud buyout, but hasn't gotten any offers near that. The other is getting offers consistent with the 6-7 bud range.

http://www.tf2outpost.com/trade/14381724 - has a 6 bud buyout. While most of his offers are hats that remain unpriced, there is one that has a definite price - a Burning Old Geezer (~3.5 buds) + 3 buds pure.

The trader was also offered a Triboniphorous Tyrannus in Disco Beat Down, which, while unpriced, will most likely be well under Harvest Moon (~10 buds) as it is not a limited effect.

The second trade, http://www.tf2outpost.com/trade/15358847, has a 10-bud buyout. His only real offer is a Power Surge Nickel Noble, which is most likely well under 10 buds given the current trend of robo-hats versus their non-robo counterparts (robotic hats tend to be lower in value). Also, if the hat were actually believed to be worth 10 buds, the first trade (with a six-bud buyout) should have been snapped up for profit almost immediately.