A good microwave will run you about $60, if you look for the right kind. More expensive ovens will give you some additional cooking options, such as “sensor” cooking, which allows you to easily cook something based on a particular kind of food and how much you have to cook. Still other ovens are called convection/combination ovens, which work on circulating hot air around the food instead of using direct heat from an element. These can be quite expensive (upwards of $400), but they can actually replace a conventional oven as well because by using convection cooking, you essentially get the same effect as a conventional oven without the open heating element. This is important: many college dormitories forbid open heating elements indoors due to local fire codes, and you can actually get one of these, get around the rules, and have an oven available to you. The “combination” side uses both the hot air and the microwave generator to cook food faster. A very useful tool, indeed.
WARNING: Do not microwave metal or anything that contains metal unless it is labeled as microwave safe.