As Sanderxpander mentioned, Sound on Sound's
Synth Secrets is a great place to start.
I know you're strapped for cash, but I can't recommend enough Simon Cann's book that scook recommended
Cakewalk Synthesizers: From Presets to Power User, second edition. Simon Cann has a bunch of videos on youtube
Noise Sculpture: Simon Cann's Music-Related Videos that you may also find interesting.
I read Synth Secrets and Cann's book cover to cover last year, but over the last couple of weeks I've started going through the book page by page while doing everything on my computer as I go along. Now I'm really learning stuff.
I started everything with b rock's
PSYN-tology and PSYN (I) on Cakewalk's Kinetic (I). PSYN II doesn't work too well on my X2, maybe because it being 32-bit (?). Simon Cann's book starts with
Triangle II for the basics, which you can run standalone. This was available free from Cakewalk, but doesn't seem to still be. See the
Triangle II download link thread for a possible solution.
Whatever you do, expect a very long process. Knowing how to program a synth is nothing compared to actually making good music, as I'm painfully discovering...