I don't know about affordable, but I've been using the Rosetta Stone program. It's totally worth it. Very user friendly & it really does what the commercials claim. The one thing is, you have to be consistent. If you go for longer stretches of time between lessons, you'll forget what you learned which makes progressing much harder. It continually builds on what you've done.
My other caveat would be, learn hiragana and katakana before you start the first lesson! I did using a really easy to learn pictographic book seen . It makes a HUGE difference in how fast you learn stuff. & helps reinforce what you're learning b/c you can pause & read the stuff even if it's not a reading lesson.
Finally, DONT use the english character option for displaying words. It will only hinder your progress. Or, at the very least, only switch to it briefly to clarify or double check something, then switch it right back to kana.
I know it's expensive, but it really is a great program. If you can't buy it, check your libraries (I've heard of several university libraries carrying the student versions).