A quick web search sort of confirmed it, but not solidly enough that I'd present the link, but I remember reading that Siegel and Shuster got the top page rate at DC, so ten bucks per complete page would be the target. No such thing as a salary, as far as I know. Did anybody have an actual full-time comic-creation job?
As Chaard points out, comic work was "slumming," hustling for a few bucks until the "real" work in advertising was available. With a glut of out of work artists on Madison Avenue, though, that wasn't a particularly good bet, either.