Welcome to EF!
As long as you don't have expensive tastes, living on around ~1300 p.m. isn't difficult. You will have some other expenses- telephone, transport cards, and commune related fees for your residence permit.
All of UNIL's cafeterias (except the restaurant) are subsidised (although I wouldn't recommend buying fruits from there- a banana costs CHF 1) and open on most weekdays. If you prefer, you can have all your meals at the cafeterias. All cafeterias also have microwaves- if you'd rather warm your food. The average cost of lunch ranges from CHF 8- 12. For breakfast, snacks, and beverages: around CHF 12 during the course of a day. And another CHF 8-12 for dinner. If you were to cook from home, I doubt if your monthly grocery bill would exceed CHF 500- unless you are the champagne and caviar sort of person