Make frequint trips to the fruit market 2 twice a week. For about $2 you can get a head of lettuce, a tomato and Cuccumber and have your self a nice big salad. Learn to make Chili. Get Hambuger and break it up while browning it, and scoop out the grease that forms. You can get Hamburger pretty lean buy doing this. Some times adding a little water while its cooking help with this. Once its browned up add some can stewed tomatoes, a can of of pork and beans, a can of Kidney beans and some chili powder for flavor. You can have your self a nice pot of chili pretty cheap. And Beans are very good for you. Get a jar of Ragu or you favorite speghetti suace and brown up the meat like mentioned earlier and serve it over whole grain noodles. Look for cans of tuna like some one said. I sometimes see them for 3 for a dollar. Make sure its in spring water. Cook brown rice put it in a bowl and dump a can of tuna on top. (thats one of my favorite but I prefer white rice but brown is better for you). Sardines are good too. a good source of omega 3 fatty acids. Get a meal replacement shake. I like Spirutein (I think thats how it is spelled). a good source of protien and it ussually less than a dollar a day. (just dont buy it at GNC) I think protien bars are a bit expensive compared to shakes. Cube steak is not a bad deal either. Yogourt, cottage cheese peanut butter on wheat bread are decent sources of protien. Make your self an eggwhite omellet for dinner. Even it you do 2 whites and 2 whole eggs. The yolk of the eggs have the vitamins Just dont stick to one kind protien mix it up. You get different Amino acids from each one.
Make sure you get some cardio in during the week, whether its running, biking or swimming or someother machine like a stain climber or eliptical. Running would be a good habit to get into considering your going to try for the police dept. Say 3 days a a week of 30 minutes of running and one day or some other form of cardio.