According to the Bureau of Labor Statistics the Average Hourly Wage for a full-time Graphic Designer in Miami, FL is $20.68
For a contract you should expect to pay at least double if not triple that. They have to support their overhead, taxes, insurance, and make enough profit to still live. When I lived in Miami I started negotiations around $60/hr.
This is for Graphic Design. If you're hiring someone to do coding then it will go up substantially well into the $100/hr range.