Based on martketplace.tf sales in recent times the pricing on backpack.tf seems not only inaccurate, but severely low cut.

If we judge it's value base on the amount in existence then it would be extremely similar to the Violet Vortex Convict Cap

https://backpack.tf/stats/Unusual/Convict%20Cap/Tradable/Craftable/131

both Convict Caps, Abyssal Aura and Violet Vortex, have 59 in existence and have similar values on marketplace.tf

Comparably Violet Vortex is worse off price wise with sales in the past year equivalent to 8-9 keys

That being said Abyssal Aura has gone up in price on marketplace in the past year and has become stagnant around $25 in recent times

If backpack.tf draws any influence at all from marketplace sales then it would be widely known that the Abyssal Aura Convict Cap should be priced higher than the 8 key price it's at now.

The 11-12 key range (around $20) is precisely for mirroring a very similar effect that has the same amount in existence (Violet Vortex Convict Cap)