I have no idea of what people earn i the US in an average job, but personally I'd "settle" for a little less if I could do what I love

when you look at the commision prices on DA (for those who list them) - there are some pretty talented people that charge 30-100 dollar for a drawing depending on color and details. The problem with both cartography and art in general is that its hard to make a name for yourself - there is lot of competition out there, especially if you go world wide.

I remember when I read in a "what can you be" book back in school. If you were lucky enough to get one of the very few spaces in the art school, you still knew that only about 5% of the students actually could live of their art afterwards - most ended up teaching art in schools or just doing something else completely.
But then again - just because the competition is hard, is no reason to give up before hand, just placing some facts on the table