[rahimnathwani]

"You have to register yourself as an independent professional which cost is around €260/month"

I think you're referring to social security contributions for (which pay for healthcare and pension etc.). The amount is in the same ball park as a single freelancer would pay for healthcare in the US.

Do you have to register as a autonomo even if you have zero income? If not, can't you build and start to validate your idea without charging money? That seems to be what a lot of SV startups do.