CV joint is usually your problem. To have one rebuilt is usually around $150. A brand spanking new one from
Tom Wood's Custom Driveshafts is about $250-300. I would recommend replacing the driveshaft if it has never been done.
A little story about Tom Wood, I ordered a driveshaft from him and it ended up going out the day after the warranty expired. I called him up and he overnighted me a new one so long as I sent the original one back to him. I have since had the "new" driveshaft in place for over 8 years and have never had to do anything to it but grease it. I also have a friend who is in the UROC Pro, Supermodified class, who uses Tom Wood exclusively for his driveshafts. They are absolutely bullet proof. I very highly recommend getting your shaft through him, his empoyoees are a pleasure to work with and will help you out with everything you need.