The blood magus homebrew you linked seems like it was based on the original Blood Magus prestige class (first printed in Tome and Blood, then later updated for Complete Arcane).
That said, the original "Blood Component" ability allowed the character to take damage to pay for costly material components, but was later edited to only allow as substitution for non-costly material components. I assume this is because being able to take easily-healable damage in lieu of shelling out hundreds or thousands of gold pieces per casting of a spell makes some of the more costly spells suddenly very very cheap to cast.
It's not a BAD idea. But the cost needs to remain a deterrent of spamming highly powerful spells, and damage just doesn't do that in a world where you can carry around a pile of CLW wands. Personally, I'd switch some of the levels and effects around on the ability.
Level 2: Reduce metamagic costs by taking 1 point of damage per metamagic level to be reduced (cannot reduce metamagic costs lower than 1 level per metamagic used).
Level 7: Pay for costly materials with Constitution damage, paying 1 CON for every 50gp (minimum 1).
Level 14: Pay for exp costs with Constitution drain, paying 1 CON for every 100 exp (minimum 1).
That said, the original "Blood Component" ability allowed the character to take damage to pay for costly material components, but was later edited to only allow as substitution for non-costly material components. I assume this is because being able to take easily-healable damage in lieu of shelling out hundreds or thousands of gold pieces per casting of a spell makes some of the more costly spells suddenly very very cheap to cast.
It's not a BAD idea. But the cost needs to remain a deterrent of spamming highly powerful spells, and damage just doesn't do that in a world where you can carry around a pile of CLW wands. Personally, I'd switch some of the levels and effects around on the ability.
Level 2: Reduce metamagic costs by taking 1 point of damage per metamagic level to be reduced (cannot reduce metamagic costs lower than 1 level per metamagic used).
Level 7: Pay for costly materials with Constitution damage, paying 1 CON for every 50gp (minimum 1).
Level 14: Pay for exp costs with Constitution drain, paying 1 CON for every 100 exp (minimum 1).