I'll second this. I routinely counsel clients to plan on spending 75/hr for a junior to mid level developer if they want someone competent, 100-110/hr for someone senior level, and 125-150/hr if they're trying to roll multiple skill sets into a single contractor or firm.

The biggest mistake you can make as a contractor is underpricing yourself. Not only does it hurt the market but you can find yourself in situations where you can't work enough hours to cover taxes, downtime, benefits like health insurance, much less a vacation. Then you start making mistakes like overbooking yourself to make up the difference and do a crappy job with all of your projects.