Invisalign is usually significantly more expensive than traditional braces. The success rate depends on your case and why you need braces. If you are correcting very mild crowding, you'll probably end up OK, but if you are correcting bite problems or significant crowding, it's probably not going to work very well.
I understand being 19 and wanting braces that aren't noticeable; it's an image thing. Braces are for young kids, and you're an adult, I get it, I really do. I say that because I had braces as an adult - I was 25 when I got mine put on. So I can also tell you it's
no big deal. And,
no one cares and
most people don't even notice!
Talk to your orthodontist and be open minded. The thing about traditional braces is that they WORK, Invisalign often leaves people with compromised results. Many people who get Invisalign end up in regular braces later on. Don't be totally turned off to traditional braces; they are smaller and less obvious now, especially if you opt for the clear ceramic ones.
Here's a link to a great site with loads of information about having braces as an adult:
ArchWired - A site for adults with orthodontic braces
There is also a message board with some really wonderful, helpful people on it who will be your cheerleaders though your treatment, and answer your questions when you have them!
Good luck, and if you have any other questions, feel free to PM me, or post back here.