How much will a GSD cost?

my mum has finally came around the idea of getting a dog. i have researched a lot into this breed and no enough (well i think so anyway) about the breed but would like to no how much they should cost i just want one as a pet so good temperament and a puppy and no that i should buy from a reputable breeder or a rescue centre of maybe evan a good pet shop but how much on average will it cost? thanks