Selling blood to wizards

I saw a bleak headline about people selling blood to make ends meet.

This has so many possibilities in a fantasy game. My games have a strong element of bleakness in them, so it's a potential match.

In GURPS Magic, you can spent hit points to power magic instead of using FP.

Losing HP can also happen from blood loss.

Therefore, blood can be part of what you expend for magical energy when you do so.

Therefore, logically, pints of blood are sources of magical energy. If you can use your own blood, you should be able to use someone else's. Especially if you have a nice, fresh pint of it handy. Preserve Food will keep blood fresh.

Mages, therefore, will buy people's blood to use to cast spells. Now we just need to set a price. Paut is $120 to replenish 4 FP. It's $5 to replenish a power item. So we have a range of $5+ for blood, and probably bounded to $30 on the upside to keep pace with the replenishment of paut. Although this is a +1. Call it $40 per 1 HP worth, because it's better to have +4 FP than get 4 FP back.

If you need after-market work to get it ready to cast, you are likely to get paid a fraction of that. Probably for the best - if your blood is worth a lot, people will kill you for it. If it's a $5 for 1 HP of blood, you're getting beer money and that's it. Again, for the better, because creatures made of money tend to get killed off - talk to whales, elephants, and gold golems.

You might want to put a cap on how many pints of blood you could cast off of at once - probably equal to levels of Magery, minimum 1. Or, you know, limit it by how terrible a person you are - maybe 1 HP worth per -10 in really nasty disadvantages. Or create a perk, Blood Magic, which allows the use in the first place. I'd probably go with the last. "Blood Wizards" buying that perk for 1 pt, allowing them to use up to Magery worth of other people's collected and prepared blood to cast spells. You'd probably get a Reputation almost immediately . . . and not a good one. No one likes a literal blood-sucking wizard.

Oh sure, maybe the loss of FP from casting spells is from the tiring process of using external mana. Maybe lost HP are just the physical loss of vitality from doing the same. But this is more fun. We had a vampyre in a previous game that had a blood-charged "power item." I may have given out another one of those in Felltower. It's been 11 years worth of play so I can't be sure. But this isn't a bad idea at all. Just an evil one.