Just remember one thing, this industry was ruined a few years ago when every man and his dog became a 'web designer'. Clients I had lined up for work suddenly turned around and said "£2,500? My nephew is going to do it for £500", or £250, or even for free just to build his portfolio. What the silly buggers all forgot was that when they wanted to start earning a living at it, there was some other young prat willing to work for free.
Remember, it always takes longer than you thought because you are dependent on the client for content, or design decisions. And they always expect modifications and maintainance for free, so build that into your quote.
If you want to make a living, not a fortune, just a living, then make sure you charge enough to allow you to do a good job. Eventually, the word will get around and people will realise that you are worth the money. My existing clients all say, "Dave, your the first IT guy we've dealt with who actually does what he says he can do".