I want to be an actress?

How do i get into acting? i really want to do it but i dont know what my parents will think if i tell them because their always like i want you to be a doctor or an interior designer or something like that but i dont want to do that, how should i tell them and get them to believe that iw ant to be an actress? also, how much money do you think and agent will cost becase ik that you have to have one. (aka im 13)