Fix it now or wait?

It's a daily driver and I don't mind a little rust, but I want to keep as much original metal as I can, and it's visibly spreading pretty fast. If I let this go for a while, will it be harder to fix (or more expensive) later? Or am I in for the same kind of repair whether I do it now or later?
Passenger side (the white stuff is old wax):
IMG_1852.png IMG_1850.png and driver's side:
IMG_1854.png IMG_1853.png