Hairdressers please!! a few questions..?

On Saturday I'm going to the hairdressers and I was going to get blonde highlights put in to my light brown hair but I want to go blonde altogether so should I get it completely dyed and then I can dye over It at hone when my roots come through? Will they have to bleach it all? Because my cousin bleached her own andher hair hasnt grown since! How much do you think it would cost if full highlights cost �50? And finally, when I dye over my roots will I have to go back to the hairdressers everytime because will the roots be a gingery colour if I try and dye them light blonde? All help appreciated, thanks