Using last month.

Sales 1-3:

Sold for $40, $22.50, and $10 on marketplace.tf

https://marketplace.tf/items/30763;5;u3005

$10 is gonna be too low, excluding.

Couldn’t find any of the item histories.

http://manicbot.me/keyprice/?at=2018-08-04 - 40/1.9 = ~21.05

http://manicbot.me/keyprice/?at=2018-08-19 - 22.5/1.9 = ~11.84

X = 21

X = 12

Sellers:

https://i.imgur.com/SoO24mE.png

19 keys:

https://backpack.tf/item/4952851421

20 keys:

https://backpack.tf/item/6987523883

25 keys:

https://backpack.tf/item/5530181810

Sales at:

12

21

The price may seem pretty low compared to sellers, but the bot.tf stats show sales around 2 months ago at 11 keys:

https://bot.tf/stats/item?def=30763&q=5&ef=Fountain+of+Delight&craft=1&aus=0&ks=0

https://i.imgur.com/WlFqzfi.png

21 is too high, given the 2 month unsold at 19. Excluding 21.

Going with 12 flat.