Understandably, many people find discussing salaries uncomfortable and embarrassing during an interview. However, most interviewers expect some bartering and, if it motivates you to put more into the job, it is worthwhile for both the applicant and the employer.
The main aim of a covering letter is to encourage recruiters to read your CV. However, it needs to do a lot more than say, 'here is my CV!'. In short, it is the biggest chance you have to sell yourself.