How old are you? Perhaps you can get a job? Or ask your parents, friends and family about doing jobs for them, to raise the money and/or earn it - if that is what they are mostly worried about. Its ok for kids to say, "I'll look after it" but they don't understand the money that goes into something like that. And they don't understand that Mum and/or dad works damn hard every day to keep you happy, and I am sure they hurt as much as you, when they can't give you something that you want. I can bet they try not to show it, but they do.
As for the click clacks, or worried about having "A SNAKE" in the house, ask them to go with you to a herp meeting. They are educational and social. Learn what the REAL snakes habits are, and not what grandma brought up your parents to believe that snakes are dangerous.
BUT, if you have to wait till you leave home, it won't be the end of the world. My parents wouldn't let me. My EX wouldn't let me but now I have them and don't care about those yearning years.