Tuna is cheap protein, and you may want to see if you can borrow a HRM. Once you've done your routine with it once, you know about how many calories, so you don't need to keep using it. If you have access, as a student, to a phys ed department or something, they might have one you could use. Generally, the cheaper ones don't measure calories, just heart rate. I think I paid about $100 for mine and it was pretty middle of the road.
And now that you don't have to be perfect, you can be good.