A kind of hokey way is to jack up the car. Run it slowly or spin the shaft by hand. As the driveshaft is spinning SLOWLY, hold a piece of chalk up to it so the eccentric, or out of round part hits it. it will leave a mark. Then place large hose clamps on the shaft with the screw part opposite the marks. You will have to test run a bit to get the vibe out. Then either leave the clamps or remove them and weld the same weight onto the shaft. A shop teacher told me this a long time and many many beers ago, so if I missed something please add to it. I did this once and it seemed to work.
For the money, just take it and have it done. Yesterday, I took my driveshaft and they cut it down, balanced it, and replaced both ujoints. total cost was 58 bucks including tax and was done in less than 2 hours. Vibrations and rattles drive me nuts....
i am a tight ***ed scrooge penney pincher. mainly 'cause i'm broke. think i sold the truck anyways... may not be my worry anymore. thanks for the tips tho! will try if i HAVE to. anymore??