how does one write a quotation to a client ?

I have been doing free-lance design work for about 2 years and I have recently been asked to do sme vector illustrations to be used on website for a company (up until this point I have only done such for friends), the company has asked me to provide them with a quote for the design and I have never had to write one before, does anyone have an example of a designer-client quote they are happy to post as a guide?