Dear Ms Li,
I regret to inform you that I decided to resign from my present position as Purchasing Manager on account of the cost of living.I must look for a job which will give me a larger salary.
Thank you for giving me a chance to learn and to gain the valuable experience during the years when I have worked under your leadership.
I will leave next Monday, and I hope my resignation would not cause you much inconvenience.
I would appreciate it if you could accept my letter to leave your service.
Yours sincerely,