What is the ruling on going to movie theaters with a mahram to watch a non-obscene national film, and what is the ruling on the money paid for that?

It is not permissible for a Muslim man or woman to frequent cinemas in their current state. Contemporary films are rarely free from forbidden elements such as music, the mixing of men and women, and the baring of 'awrat (private parts). The prohibition is not limited to the presence of indecent scenes.

If one is prohibited from entering the cinema, it is also not permissible to spend money on this forbidden amusement, because it is spending a blessing from Allah's blessings on something Allah has not permitted, in fulfillment of His saying, the Almighty: (And do not squander wastefully. Indeed, the squanderers are brothers of the devils, and ever has Satan been to his Lord ungrateful).

Squandering (tabdheer) is spending on what is not rightful. Even if one were to spend a "mudd" (a small measure) on what is not rightful, they would be considered a squanderer. It is spending in disobedience to Allah the Almighty, on what is not rightful, and on corruption.