pullies usually rely on each other
here is a pic of my pullies
you are probably talking about your a/c compressor being seized. you should be able to get one from a junk yard or pep boys for about 50 bucks. installation will be 100. if you want to try the cheaper route, go to lowers/home depot and buy some liquid wrenches. that will unsieze anything. i would try plan a first. since if you break a belt, you are usually stranded if not instantly, you will be when your battery dies.