What to charge for freelance work: ask the expert
This is a good question. And my advice would be to go to market with the rate you have quoted - as this must be the rate you feel comfortable charging - and wait for the response. If clients accept this rate, great. If clients tell you they are being offered lower quotes from other people who have comparable expertise and skills to you, decide first how much you want this client's business and then make a call on adjusting your rate. If a client wants you enough, and values your reliable and quality service, it will take more than cost to attract them to another provider. Aim to compete on quality, not cost.
On a final note, you might be interested at an online hourly rate calculator developed by the good people at Freelance Switch. You can check it out at http://freelanceswitch.com/rates
Hope this helps.
Emma Jones is Founder of Enterprise Nation and author of 'Spare Room Start Up - how to start a business from home'