Should I mention salary when I explain why I want the job?

Not in the motivation answer. Money is a legitimate reason to want a job, and an interviewer knows it, but saying it as the reason invites the question of whether you would leave for the same amount elsewhere. Keep the motivation answer about the work, and let the salary conversation happen when they raise it; if they ask directly, answer briefly and return to the role.

'Why Do You Want This Job?' in English Without Sounding Rehearsed →