I second synth1,Mutant wrote:Learn the freeware Synth1, save the 200$ for the time when you will know what exact payware synth you need.
While all the other suggestions sound great this one is basic to a positive point:
It is raw subtractive synthesis which enables to learn the basics of soubd creation.
With all the knowledge that you can learn from this you will be able to create great sounds on any synth,
And have an easy time to learn the most complex features that are available in other synhs.
Cheers
Thor