Blood Mages;
Prestige, Variant Class, or unplayable?
Prestige. Blood elven archmagi.
I'd consider it a variant of the Archmage prestige. They have the political power of an Archmage, but they use different styles of magic, as Blood Mages dabble in Fel a fair amount.
Blood Mages actually have fairly different powers from an Archmage. Also, Blood Mages are far more distrusted by other races because of their use of Fel. A big part of prestige is the attitude/reputation/influence your class has. So I would consider it a prestige of its own, and not a variant of anything else.
I've seen Orc Blood Magi. Is it really only Elves?