Ask the people who teach Web design and see if their students would be willing to take on my business as a class project. Even though they're not professionals, students are highly motivated and creative and they don't charge a lot. I learned HTML myself and did my own Web page. It's not hard. I do a lot of research and find out what other consultants are charging for similar work.
Some fields charge hourly, some charge per project.
It's hard to say not knowing the field you're in, but ask others in your field about what they do. When you're first starting out, people are more willing to take a new consultant if you're charging at the lower end of the range. But if you're too cheap, they'll think you won't know what you're doing. Consultants can be internal and external. Internal consultants work for companies.