I also agree w/ what's been said so far. As for taking a class, it's definitely a good idea. However, if classes are a bit expensive for you, go ahead and start studying on your own. It can't hurt! At worst, you'll realize you're not as motivated to learn Japanese as you thought you were, and you'll give up. But I suppose it's better to find out now than after you pay $$$ for a class, ne?

And, if you're very motivated and disciplined, you can surely learn a lot on your own, and invest in classes later on if/when you decide you're ready for it.
Other than that... Just set your goal and put your heart into it! It's easy to get sidetracked by thoughts like "Maybe I'm using the wrong method to learn Japanese" but if you put in enough time, you will get results.
Personally I'm learning Japanese on my own, here are some things I've found useful:
1. Good textbook: Japanese for Everyone ($18) or Genki ($25 x 2 volumes= $50)
2. Kanji Pict-o-Grafix: great book for learning 1200 kanji. (beyond that you may decide to buy a different book, but for starters I really recommend this one)
3. Listening practice: If you can afford it, the audio that goes along with your textbook is always a good idea. (may be able to find online!) There are good videos made in the 80's called "Let's learn Japanese", which are nice because they speak Japanese at full speed so you get practice trying to pick out individual words.
4. Flashcards!!! Either real flashcards or a computer program like JFC.
5. Japanese IME... If you don't already have the capability to write Japanese characters using your keyboard, you should install it...
Good luck!