2,750 g
This item page for Hemomancer's Helm reflects public Arena Mayhem data for patch 26.19.
Unique - Scarlet Allegiance:
If your life steal and omnivamp sum to at least 30%, gain 500 bonus health and heal yourself equal to 10% of the damage that enemy champions within 525 units of you take from all sources.
Scarlet Allegiance activates as long as the user's life steal and/or omnivamp values equate to 30%.
The effect adds both values and determines if the sum is greater than or equal to 30%. If it is, then the effect activates.
It does not require either value to not be zero; it will still activate if the user's life steal is 30% and omnivamp is 0%, and vice versa.