no seriously there has been.
"There isnt an 'average' rate because demographics are too widespread. With this in mind, you can find your rates by doing the following formula"
"For this forumla, you will ned to figure out what your overhead is. Overhead is an expense that cannot be billable to a client.."
"Lookat these areas... (rent, Income tax, utilities, insurance, supplies, marketing, shipping, telephone, accoutning, legal, travel, furniture, dues, licences)"
Im not entirely sure how much of this applies but was taken from my freelance research work I did a while back. These were the general costing issues when it came to finding a salary as such.