GURPS Undead Creation

[Darkholme]

So, I'm having a bit of a dilemma.

I'm putting together a GURPS campaign.
I'm using RPM, more-or-less, with some variants found in Pyramid, like incantations.

Anyways.

I want to be able to create undead or otherwise affect permanent change on subjects or inanimate targets via magic.

So a necromancer might be able to make himself into a lich, or unleash a bunch of ghouls/wights on the world (which can then create more ghouls/wights), or magically create a vampire, or what have you.

I'll probably hand-design the spells I'm willing to make permanent rather than let the PCs design them, but I don't know how to price them out reasonably.

How would I price out a spell that makes an undead creature, that isn't a temporary effect. Not an undead creature permanently under your control, just an undead creature (controlling it would be a different spell you'd have to maintain).

RPM doesn't have pricing for such effects. So how would I price it out if I wanted to include such things?