Don't know about $, but over here the Creative X-Fi Titanium Fatal1ty Professional can be gotten for £80, so that should fit snugly into your budget.
I have one myself, and I can say for sure; I'm never going back to integrated sound cards. Once you have heard the difference, it will pain you to go back to integrated.
That is, supposing your speakers/headphones are up to snuff. When you have more dosh, I'd recommend a few studio monitors as well.