Well, it varies - I've been quoted anywhere from around $100 to over $5,000 for both art pieces and full cover design layouts. There are plenty of lower rate freelancers on gig job sites (Behance, etc.), but the quality v. cost math hasn't added up yet. At least the ones I've run across also seemed to be reusing pre-made material and/or seemed more interested in promoting their personal style than working with our branding requirements, both immediate no-go red flags for us.