I wasn’t French when I studied here. The tuition was still pretty low, roughly 800€ year including insurance afaik my school did not distinguish between local and foreign students. More known schools like ISEN or EPITA took roughly 5k€/year afaik but I may be wrong.

Granted, I didn’t go to a prestigious grande école, rather just a “pretty good” engineering school. Also business schools are indeed more expensive than technical degrees. Not to mention that Paris region is way more expensive than the rest of the country.