Potatoes can be the backbone of a frugal diet. I have been eating more of them since I discovered the microwave potato chip recipe. Sweet potatoes deserve more attention, however. They are more costly and far less storeable than regular potatoes - they can easily go bad within a few days - but they have nearly two times the food value of white potatoes and only about half the calories, with a bonus of sunrise colour and flavour. They can be a main course or complement a vegetable, protein, or grain dish. I can usually find firm, reasonably priced (though small) sweet potatoes at Jia Hua (Chinese Superstore).
One of my favourite methods with these is to cube and toss with some olive oil, salt, chopped onions, and red pepper and bake uncovered in the oven til vegetables are soft and browned and flavours are mixed. Also, a very fast way of preparing sweet potatoes is slicing them thinly and single-layering them on a flat pan, drizzling with a few drops of olive oil and salt, and broiling. Keep a close watch because the high sugar content makes them likely to burn quickly. I like to broil both sides, but it is not necessary. The best way to eat these is to dip them in mayo and sip a cool crisp white, but sour cream and a homemade lime soda works too. (Squeeze a lime's worth of juice, mix in sugar and salt to taste, and fill glass with soda water.)