Having no budget is a creative brief too. Some of the best videos online were shot on a cracked phone.

A budget of nothing removes a whole set of choices and sharpens the ones that are left. You cannot fix a weak idea with production, so the idea has to carry it, and that pressure makes things clearer. It is a constraint like any other, not a virtue and not a disqualification. Plenty of work that reached a lot of people was made on whatever was already there.

Write down exactly what you have: the phone, the room, the two friends who will help, the free software. Treat that list as the brief. Then make the thing inside it rather than waiting for the version that needs money.