My 2.5 mth old kitten is limping any advice?

in a matter of 4 hours she went from being super playful to limping. her back leg seems to be giving her trouble. shes still eating and shes trying to play with her toys. and even jumped onto the couch. i have tried to look at her paw but shes not coopertive (even b4 this) i called the vet and its going to cost a fortune for xrays ect.(would be emergency room visit) we are on a tight budget and cant afford a visit .we are extremly worried about her and want to do whats best for her. i am starting to think jynxie wasnt the best name for her this is the 2 issue in 3 weeks >.<