It's going to be difficult, but if you only eat at home and only buy foods that you are suppose to eat, it get easier. Once you start eating out or hanging out with friends for prolong amounts of time, that's when you will have cheat days.
Not to mention, special diets are costly. If it gets tight suddenly, you are going to have to break down and buy cheap comfort foods just to get by. That's the reality of it all. Economic dictate everything.