You write salary requirements in a cover letter by stating “my salary expectations are negotiable depending on the overall compensation and benefits package” toward the end of your letter. Alternatively, if you’re asked to specify a dollar amount, simply include a sentence like “my salary requirement is within the range of $35,000 to $40,000.”
However, mentioning salary expectations prematurely can hurt your chances of getting hired, so only include salary requirements in your cover letter if the employer requests it.