If your have so much problems keeping enough mp with just blood price well then your doing it wrong once youv secured hate on the mobs you start using your siphion blade and soul eater combo to regain mp and hp then do a combination of your hate generation combo and soul eater. And blood price is great for when your doing mass pulls because while their trying to kill you your useing unleash to secure hate and blood price is getting you mp back from all them trying to kill you.

Its also good to be useing blood price in boss fights because then you can be useing more dark arts buffs.