Does this help?
Let alone what artists were typically paid for similar creations at the time?
There weren't really similar creations at the time, comic books mostly reprinted newspaper strips and people who created new material specifically for comic books didn't make a lot. The effects of the Great Depression were still keeping wages low.
The creation of Superman essentially kicked off the comic book industry as we know it today, for whatever that's worth.
I may have gotten the details slightly wrong but it's been decades since I delved into comic book history.