HELP!!!!!!! My dog won't stop limping!?

Okay so today my stupid sister took my dog to the park. She took him on a slide, and something happened to his leg or hip. He's in pain I can tell, because he won't stop limping. When he stands, his back leg keeps twitching and he raises it slightly. I honestly, don't know what to do. My mom and I hope his leg isn't broken or his hip is displaced. Going to the vet is costly, and the vet will probably want to take xrays and want lots of money for meds. Is there any way we can help him, at home? Like is there any pain medicine we can give him that we humans take too? Or what if we wrapped his leg in gauze or something? PLEASE HELP.