[nederdirk]

I have totally no experience with this, but I would use a search algorithm to establish your 'real rate'. Decide for yourself what figure you need to earn as a bare minimum and try to sell your services for that price. After getting a job, you know one price you're not worth. Raise your offer price by twice the amount you think would be fair and try to find new work. Measure and write things down, as far as possible avoid selling for the same price twice, don't lose confidence in yourself.

Add: Don't listen to me, davismwfl's advice is better.