Beep Box Midi Music Maker, say that five times fast.
I don't know how to make music, but when the only person you can hire to make your game is yourself BeepBox is a tool that gives you the ability to help yourself. You see, BeepBox is kind of like training wheels for a tuba. When you have all the mice and men making electronic dance music you think, how hard can that be, then you try it yourself it sounds like a pile of poo. Anyways, what I was saying was that BeepBox is the place to go for making simple tunes that add a lot of color to your game. Easy to get something sounding good and I'm sure for more advanced users it offers depth to make more complicated music. I wouldn't know because I'm not an advanced user, but who is really.
If you give it a try yourself, you'll see you can add notes at different points. Yadda yadda yadda. Like I said I don't know how to make music, but open it up and start clicking away and you'll see how fun it is and how great your songs sound. After all, they say even a monkey can write Shakespeare when given enough bananas and time.