Cleaning off rust? Or is there no hope?

I have a crappy bike that I bought about two years ago, because I wanted a bike, but it was all I could afford at the time. It was about $300.00, hybrid/mountain thingy made by Iron Horse. In my old apartment, my room was gigantic, and so I stored it in there. The place that I've lived in for almost a year now is not so big and there is definitely not enough my room in my bedroom for it. My sister didn't want me storing it in common area because she said it looked ugly, and there isn't a bike storage room or anything in our complex. So we have a small balcony and I stored it out there, though I was hesitant, but I had no choice. For awhile it was fine. But I went out to check on it the other day, and noticed that the chain and the gear thingy (I think that's called the cassette??) are a bit rusted. They're not horrible, but I am wondering if there is any way to clean them? Or are they busted and I would have to replace them? I may sell the bike when I get my road bike (which will live inside, come hell or high water!), so I want it to be in good condition regardless, even if I end up keeping it- I'm moving again and depending on where I move, I might have space for both.

Any thoughts? If I can clean them, what should I use?

My city bike, which is a big hybrid, also sleeps outside, and is quite rusty. I oil it once in a while - which makes it look better - but I haven't bothered cleaning the chain.

DISCLAIMER: I'm no bike mechanics.
If you really wanted to clean the chain on the cheap, you could use WD40 and a good brush with hard bristles (found in any bike shop). A tooth brush is not bad but I usually find them too soft. (Maybe if you buy the "hard" style it would work better?). Make sure you rinse with water when you're done and oil very well.

I wouldn't use WD40 on expensive road bike components, though.

Thanks for the advice! And believe me, when I get my road bike, not only is it going to live inside, (and covered with a tarp or something, if it has to live in a garage/storage area), I am going to take verrrrrry good care of it :) I know there's all sorts of stuff to keep it maintained- my ex had this stuff that he'd squirt on the gears after every ride. I'll be sure to ask the guys at the bike shop what I should be using/doing.