Web designers, like most other professions, pay depending on the projects that you do. If you are an independent web designer freelancing, you can charge depending on what the market will allow (and how skillful you are). From what I've seen, this hourly rate can be anywhere from $30/hr to $60/hr. Some projects will also pay upon completion and each will be negotiated separately.
If you work full time at an agency as a web designer, it will again, depend on your experience and skill level. Entry level web designers can usually make between $40,000-$60,000 a year salary.