Hi i am also a poor student and feel your pain. however i am a tech student and can probably help you.
1. Look at your battery connections. Is there gunk/corrosion on the clamps or around the battery terminals? Also make sure that the clamps are tight on the terminals. If there is corrosion, buy some battery terminal cleaner from walmart, clean the terminals and clamps then tighten the clamps. If this doesn't help take the whole battery to walmart, or an auto parts store and have them test the battery. They will let you know if you need a new one.
2. If the battery is all fine, it is most likely the alternator. If your alternator is bad then you will have no power whatsoever throughout the car. If it was the starter only then you would still have power to use the radio, blinkers, lights, pw/pl/ps and so on. Take your car to an auto parts store and ask them to check your alternator. They can tell you if it is putting out enough amperage or not. If not this is a fairly cheap fix, $75-$125 depending on what type you purchase, and it is very easy to replace. There may be instructions in your service manual if you need help. All you would need is a socket set to change out the alternator.
email me if you have more questions david.winter@hotmail.com
Hope this helps