I'm gonna try this again. Turns out that 17 buds seems more of an outlier.

Previous sales:

Sold for 10 Buds + 10 Keys (0.6) + Black Bills (0.4) + PE Fuka (3.5) + G.Fetti LuckyShot (2.3) + 99$ (3) ~ 19.8 buds

http://www.tf2outpost.com/trade/19994339

Sold for a hearts modest (11) + scorching frenchman (4.5) + ghosts elfin (3.9, old price) ~ around 19-19.5 buds depending on the elfin:

http://www.tf2outpost.com/trade/20679927

http://www.tf2outpost.com/trade/20905295

Sold for a clean lantern buto (8) + clean lantern stash (10.1-14.8) ~ makes the pyromancer around 19-20 buds, close enough:

http://www.tf2outpost.com/trade/20062877

http://www.tf2outpost.com/trade/19749005 - mancer was offered

New sales:

Sold for KaW TC + Miami Bonk + Scorching Whoopee ~ 20 buds (seller's b/o):

http://www.tf2outpost.com/trade/21301587

Duped one sold for 18 buds pure:

http://www.tf2outpost.com/trade/21416608

added 4 buds for clean burning mancer ~ 20 buds:

http://www.tf2outpost.com/trade/20674503

Outliers:

Sold with 30 keys for a duped burning modest (which he later qs at 17 buds) ~ 14.9 buds:

http://www.tf2outpost.com/trade/21265147

Was QS at 16 buds, added for a roboactive muffs which was QS at 17 buds:

http://www.tf2outpost.com/trade/21284351 - mancer

http://www.tf2outpost.com/trade/21107641 - muffs

sold with SBTWC merryweather (6.2) for C.moon cannonball (18.9) + DBD phantom (7.7) + sulphorous flamenco (7.7) + 1 bud 6 keys (1.4) ~ 28.6 buds:

http://i.imgur.com/MvuPLVl.jpg

The Burning Bat merryweather price was accepted in the ghost mancer pricing to be valued at 6.15 buds http://backpack.tf/vote/id/53a952334dd7b82b488b4771

GE mancer + scorching mancer + burning Guadalajara sold for a duped Secret TC(55.4*0.9) = 50 http://www.tf2outpost.com/trade/19752826

So there's 2 sales at 19, 3 sales at 20, 1 duped pure sale at 18, 1 sale at 17 (ghosts muffs), 2 sales below 17, one sale at 28.6, and one sale at ~ 25 buds.

19-20 seems about fair.

Also, about this sale:

http://www.tf2outpost.com/trade/20684132 - scorching mancer + 1.5 buds for ghosts muffs.

When Polar closed my previous suggestion at 19-20 buds because he mention that the muffs sale was around 17 buds, I found out that this sale should be considered an outlier instead, and here's why.

In the muffs suggestion http://backpack.tf/vote/id/53c7c86c4dd7b8892e8b456 , the scorching mancer sale was used as the high end. If we were to exclude the mancer sale, the price of the muffs would be at 15-17 buds. Considering that 1.5 buds was added alongside with the mancer for the muffs, that will actually price the mancer at below 16 buds, which is a clear outlier.