i contribute weekly to one project, but i am not a maintainer. i could reason that my contributions to this project are worth money. being paid every month would be reasonable.
in another project, i only contribute when i run into a bug or need something added. this happens maybe 3-4 times a year. i could reason that these bug fixes and feature additions are worth money, but i would be out of line to say that a monthly amount of money is reasonable. do one time donations or 1-2x a year donations make sense?
i also have various projects where i've contributed 1-10 lines of code once and never come back. i don't deserve to be paid for those, in my opinion.