US $18,000 a year isn't the primary income, but it's more than a hobby, too.
And 30 pages a month is a lot of time commitment, too. Simpler pages than many in panel count, but fairly detailed art... For comparison, most full-time webcomic artists I know are doing 3 pages a week, 12-13/month. A standard superhero comic is 22 pages a month, but that's with separate people doing writing, penciling, inking, coloring, and lettering. Terry Moore did Strangers in Paradise on his own, 22 black and white pages + self-publishing work; that's around the high end. Questionable Content is 5 pages a week, but they're usually 4 panel pages with simple or re-used backgrounds.