Because you are underage, starting HRT is a lot more complicated than it is for an adult. HRT involves the administration of some very powerful drugs that will have a permanent effect on your reproductive system, as well as many other parts of your body.
IDK where you live, but I have not been to a place yet where a doctor can prescribe or administer drugs to a juvenile without signed, written permission from at least one parent, or, depending on the laws where you live, both parents.
I imagine that if you talk to your doctor about this, your doctor will tell you the same thing I just did.
So, like it or not, if you want HRT, you have a choice between coming out to your parents, or waiting until your eighteenth birthday.
As far as cost goes, if you are living in the U.S. your parents' health insurance should cover HRT if their plans are compliant with current federal law.
If you have to do this after you turn 18 without your parents' help, then you need to learn how to apply for federally subsidized Obamacare, and you need to get a job to pay for the things that insurance does not cover, like hair removal and facial surgery. (Since you mention crossdressing, I am assuming you are MTF).
I keep having to give this advice over and over, but the absolute best thing you can ever do for yourself, once you turn 16, is get a work permit (if you need one) and get a job. If you have no income, you are dependent on others for everything, and that is a bad position to be in when you are transitioning. With a job, you have income, you have options, and when you are older, you have a good work history that will pave the way to better opportunities.
