Im sorry...but I, being a designer who has done both consulting and full-time work and 'likes to think' he tries to solve the customer's problem first and foremost, find this rate of $300-500/hr extremely high. Has anyone else heard of numbers like this being made, be that full-time or consulting?
move upmarket. A small dotcom may now be able to pay $300/hr but when you're setting up an independently regulated financial utopia (See the independent finance centre of the americas) a few shekels for design is nothing.
I have no doubt sites like national geographics website cost over a million. Just like a good iphone app costs $200K+ good design costs, and is exceedingly rare.