Blood Money

You can cast Blood Money as a reaction just before casting another spell that requires a material component. As part of this spell's casting, you must use the small knife or blade to cut one of your hands, releasing a stream of blood that causes you to take 1d6 slashing damage.

The damage occurs when creating any inexpensive material component. However, when you cast another spell in the same turn that requires a costly material component worth more than 1 gp, the cost is more severe. You gain one point of exhaustion for each 500 gp worth of the component's value. Even valuable components worth more than 1 gp can be created in this manner, but the exhaustion cost is substantial.

Material components created by Blood Money transform back into blood at the end of the turn if they have not been used as a material component. Spellcasters who do not have blood cannot cast Blood Money, and those who are immune to exhaustion (such as undead spellcasters) cannot use Blood Money to create valuable material components.