I feel like a lot of magic girls' skills would either be extremely niche or unmarketable.
Mm, that's kind of questionable?
Okay, so, the current population density of magical girls seems to be around 1 per 100 000 people, so around 70 000 magical girls globally in total.
By way of comparison, there are around 100 000 specialist surgeons globally - so magical girls would be rare specialists.
At bare minimum, magical girls are supernaturally skilled combatants who can literally be paid to eliminate sources of depression in cities, and who given time can heal any mundane wound.
That's an extremely attractive skillset already, to the point that almost all local governments would happily pay to keep some gucas on retainer, and it isn't even getting into specialized magic.
The only reason healing magical girls won't make entirely ludicrous amounts of money (they can
reverse aging) is because they're relatively common. I still expect them to make "experienced brain surgeon" amounts of money, easy.
And girls like Inoue Yuki, who have a very rare power with incredible global applications? She can literally write any number she wants on a piece of paper - she's a bigger strategic asset for most countries than a
nuclear submarine.