CV and possibly a Cover Letter

Hi, I would like to create a CV from an existing resume I have, I am Canadian and applying for only one position in London, and this will be the only time I ever use a CV, so I don't want to spend an excessive amount. Do you have a deal for doing a CV and a cover letter? and how long would it take? and Have you ever written a CV for a position with the government (The Commonwealth secretariat) before? I have attached a job description for the job I would like to apply for, I need it done by the 16th of april.