I've run for office, and yeah, the running is a job all on its own. That and everything takes money.
Campaign signs don't print themselves, canvassers need to be paid, handbills need printers, venues need to be booked, offices need to be rented and all of it, all of it takes money that the majority of candidates simply don't have on their own.
Once you experience that you realize why a lot of politicians become corrupt, or at least corrupted by the system.