I cannot remember whether I offered Spell Slots, doubled cost after chargen or both.
Not a fan of Double after Char-Gen. That turns them into Positive Qualities instead of Magical Abilities.
But I could see them being even more than 5K, 7-8 isn't unreasonable IMHO.
Though at 5K they are a nice option to exchange with spells in the CG process.
Actually, I just thought of an idea, it gets kind of complex but, I think it could work.
PP Cost is 8, Pre & Post Gen, up to your Magic Attribute.
Spells Can be Exchanged for PP at a cost of 3 Added Karma.
Now your talking some really diverse set ups at Char-Gen for MA's. They can have Cash & Qualities & Full PP but would sacrafice spells.
They could have a mix of lower levels of them all & bind a foci too, & still be able to grow after CharGen as Adepts & Casters.
So for example, just off the top of my head something like this.
Focused Concentration-4 (16)
Mentor Spirit (5)
3 Spells (0)
2 Power Points for Spells (6)
2 Power Points (16)
7 Karma to Cash = $14,000
Sure, I could build that same build now for 48 Karma & have 2 More spells, but I couldn't grow those last 2 PP ever.
I kind of like the idea of a little more diversity at Chargen & with growth but having the costs be a bit higher.
I also kind of like that it might lead to more situations like you had in SR2-3 where someone was only partially good at both the Adept & Caster sides instead of able to do both of them awesome but w/o any positive qualities or cash or skills.