Well, if you're going to buy a sewing machine, be prepared for sticker shock. I saw one the other day that cost $6000. On the other hand, the really cheap machines are junky and will frustrate you to no end. Medium grade machines like the one I have cost about $700. Could you borrow one from someone for a while? Or maybe you have a friend or aunt or your mom who would let you come over and use hers. You could also look for a used one, but I had no luck with that. Of course, you could sew by hand, but that takes forever.
Before you even get your hands on a machine, go to the library and get a couple of books about the basics of sewing. Then you could buy a simple pattern like an A-line jumper or sundress and give it a go. Don't let your first project be one that requires a knit fabric, or one that calls for something slippery or very thick fabric like denim. Knits are tricky. I've been sewing since I was 6 years old and I still avoid knits. Another route you could take is to sign up for a class at a local fabric store. The smaller, locally owned stores often hold classes. Generally, you pay a fee for the class, and sometimes you get a discount if you buy the materials you need at the store.
Also, when you do attempt your first project, pay careful attention to the instructions, and don't skip steps like ironing your seams. And always prewash your fabric! Good luck.