What year? And like extreme asked, are we talking front or rear?
I just recently replaced all the ball joints and the right front spindle on my 88 Formula. You have to take the spidle off to replace the balljoints, so it's not any more work to replace the spindle. I found a replacement spindle in a junk yard for $45. Rodney Dickman has ball joints for all years, and you'll need to rent or buy a ball joint press.
If you have any questions, let me know. It's not a difficult job. You will have to remove the front spring, so be sure you have some chain to secure the spring when you're removing it.
Check out this thread for some great description and pics of a rebuild. It's on an '88, but it should give you a good idea even if your car is a pre-88.
[This message has been edited by Formula88 (edited 10-21-2004).]