From the sound of it, you're crash-dieting. Don't do that.
So, you want a diet suited for a heart problem, and it has to be cheap. Here's what ya do.
1. No coffee. Bad. It's a stimulant, like all weight loss stimulants, it'll boost your metabolism... by speeding up your heart. Not a good idea for a heart condition.
2. For breakfast, have a slice of toast, with some cut up fruit on it. This is cheaper by far than cereals. Eat with a cup of green tea. Green tea is fairly cheap too, and has antioxidants, which are good for your heart.
3. For lunch, have your big meal for the day. If you must have frozen food, invest in some tupperware, and freeze your own. Lean cuisines, if I recall, taste lousy for the amount of calories they have, and tend to have quite a bit of salt. Lean cuisines also cost a LOT more than homecooked.
Make this meal have a serving of protien, a serving of complex carbs, and a vegetable.
4. For dinner, have something light. A salad with ranch dressing, for example.
5. For dessert, a little dark chocolate. A little won't hurt that much in calories, and the antioxidants will do you good.
For when you get hungry, try unsalted nuts. Peanuts in the shell are pretty cheap, and are much better for you than peanut butter.
In general, while cooking, avoid salts and fats. Try to use more garlic or avocados. You can also have egg whites and low-fat cheese.
You CAN work out with a heart condition, in fact, that's one of the only ways to make your heart stronger. If you can't get a heart rate monitor, learn to take your pulse. Every now and then, while working out, take your pulse. If it's above 130, slow down.