From the advice I have from what is one of the most successful design companies in Aussie, the CEO suggests charge what it's worth to the client. Talk to them about value, how much money it will make/save them. But at the same time don't undercut your prices, the prices above are about right, just make sure you do not underbudget time. That is the easiest mistake to make.
Also, when you present the cost to the client, be sure to justify it. Tell them how it will make/save them money, why it is such great value. Show them the development process, break down the time into tasks for them. Just make them feel it's worth it. Say why you are better than Joe Bloggs. Oh another very important thing is to make them trust you. Be absolutely as professionally as possible.
I'd suggest this book, I've purchased it and it's great:
http://www.sitepoint.com/books/freelance1/ . It basically walks you through setting up your entire web design business, whether to go freelance or as a company, how to market, invoice, deal with clients, etc. It also has some useful real life examples and templates for tons of different marketing letters and invoices and so on (although I will never use the marketing letters as I don't like the hard sell technique).