Having been the artist in this relationship many times, I'll tell you what my rates typically are: £20/$30 per hour. I'm a freelance professional artist and graphic designer of 10 years, so I like to think I have a relatively good nose for the going rates. Mine are considered to be on the cheaper end of fair in the professional sector. It can go up - especially in the city, or down with new graduates or students. but to be totally honest it depends on what you're willing to part with financially. And what kind of job you want
EDIT: Additional - Just don't use sites like fiverr - they're killing the rest of us! Good luck on your quest.