Not many of these left to update.

New price: 7.5-8 keys

Proof:

Sale #1 (3 weeks)= 8

https://backpack.tf/profiles/76561198011321852#!/compare/1529798400/1529884800

Sold for 8 keys 9 ref. Rounding to 8.

bot.tf sales:

https://bot.tf/stats/item?def=1119&q=5&ef=Hellish+Inferno&craft=1&aus=0&ks=0

https://imgur.com/a/pBm2KjH

https://backpack.tf/profiles/76561198305676157#!/compare/1524088800/1524175200 - 8

https://backpack.tf/profiles/76561198344933095#!/compare/1524693600/1524780000 - 7 keys 20 ref = ~7.5

Marketplace.tf sales:

https://marketplace.tf/items/1119;5;u3013

Sale #1 (2 months) Sold for 10.06$. Keys were 1.98$. 10.06 / 1.98 = ~5

Sale #2 (3 weeks) Sold for 20.00$. Keys were 1.93$. 20.00 / 1.93 = ~10

Sale #3 (3 weeks) Sold for 19.89$. Keys were 1.90$. 19.89 / 1.90 = ~10

Sale #4 (2 weeks) Sold for 19.90$. Keys were 1.92$. 19.90 / 1.92 = ~10

_________________________________________________________

SUMMARY

Sales:

5 x1

7.5 x1

8 x2

10 x3

5 countered by buyers.

Unsold for 2 months at 9.74 keys. Excluding 10.

Going with 7.5-8 keys.

Feel free to add proof to support or counter my new price.