The rate depends on your skill level for the most part.
What I do is itemize and estimate time for the project, then apply my hourly rate to it + costs (like photography, copy editing, whatever). What might take me 100 hours, may take you 150 hours, and my time might be worth $40/hr and yours only $20.
The question you have to ask yourself is really, are you worth it? Would you pay you for the service you're offering? Do you have the experience to really bring value to the client?
All that having been said, I normally charge around $4,000 for a site that I can finish in a month.
Normally there is no any universally accepted formula for pricing, it actually requires the decision to make the judgment concerning the business conditions, competitive reactions, the target customers, cost of the project, and your business goal.
Overall you should be able to convince the customers that the price you are going to charge is rational and apparent and it's going to match with the service and support you are going to deliver or render.