Assuming that you want to make synth oriented music by your post on this forum, the cheapest way to start is to search for free softsynths (software synthesizers). One of the more advanced but freely available ones is Jeskola Buzz
. The only downside is that it's not super user friendly, so you need to be willing to figure it out.
If you want something more user friendly and accessible for a beginner, you might try Fruity Loops
. You can download the demo for free, and full versions with varying feature sets start at $49. There are lots of tutorials and user forums available on their site to help you learn to use it.