Just to have a comparison: This is exactly the same value as the soul of a Scamp or an Ancestor Ghost.
Vivec has 1000 and Almalexia 1500.
I am going to mod this up in my game. What do you think: is 600 reasonable? This seems semi-devine (as an Aspect of a Deadra Prince should be) while still being able to fin in a Grand Soul Gem.