Ok...
I wish I knew something about jazz to help you out, I think it's great that you have the interest and desire to get into this music, but I know nothing about it (yet).
I don't think you should be so quick to discount books and a teacher. I got my first job at 14 (<14 was illegal, child labour), and that was all disposable income, as opposed to having to pay rent, insurance, groceries, etc... Meaning it was a lot of spending money. Even if you can't get your own income, it would be worth getting the help of your mom, as much as you might hate it. A teacher is the best way to go. Also, you could go to your public library to find books ($10/year for library card where I live).
To find a teacher: word of mouth. Spread the word that you're looking for a teacher. Somebody will know where to point you. Be willing to call up people you don't know in your search for a teacher. It's what I had to do. Slightly nervous, but it's what it takes.
Now I wonder, what do you mean when you say you have no idea how the notes/rhythm works? Do you know how to read music? Give us some background on your abilities, so we can help you better.
If I were in your shoes I would go straight to the jazzband teacher first thing Monday, tell your situation and what you want to do, and hear what the he has to say. If anybody knows what it takes to join the jazz band, it's the teacher. Even if you can't immediately join the band, the teacher will be able to point you n the right direction. This is also the best place to start looking for a private teacher.
Jazz is good stuff, and a lot of fun by what I've heard. I hope you can enjoy it, and I look forward to the day I get to dip my toes in those waters.
