I just got my braces off in January, at the terribly old age of 27. I know it's not old, but believe me, it felt old every time I went to that office full of teenagers!
My treatment, total cost including the first set of retainers was $3950. I also had to have wisdom teeth out first, that was about $1500 more. I can say it was well worth it, I feel much better about myself now. I had to do it as an adult because my grandparents raised me and they just couldn't afford it. I had to pay for it all, because our insurance wouldn't pay a dime since I was over 21 when I got them on.
One thing of caution (don't want to start a debate, it's just something I think is not good), one of the orthodontists in my town (not the one I went to) is starting to put braces on children at the age of 7 or 8, leave them on a couple years, then when all their permanent teeth come in, he puts braces on them again when they're 14 or 15. I don't know much about orthodontics, but I wouldn't want to pay for it twice (and he does charge the same fee twice, around $4000 each time), I'd just wait until they were 14-15 to do it.
My SIL got hers on when she was 15, and she went to a general dentist for it, and only had to pay $2000; you might try that route, although I'm not sure how severe of cases they can do.
Good luck, it's expensive, but it's worth it!
Steph