I'd suggest planning out your language. Talk about seeking treatment and not wanting to rush into things or make rash decisions. The conservative approach promotes confidence in your decision to seek help.
Research the therapy here first though. Parents often try to corner their children and get to the heart of the issue quick with as little BS as possible. So be prepared by doing the research first.
Where I am I see a therapist about once a month, she is okay with others attending the sessions so long as I approve first and give her advanced notice. Your parents will want to know about cost and some insurers will cover it but I recommend finding and experienced therapist with gender identity experience first and asking them how they handle it. Mine knows quite a few tricks in the medical coding world such that she can be paid and I leave no trace of my gender identity issues. After all I do have anxiety, my gender identity just happens to be a trigger for that anxiety

Fees from my therapist are about $120 for an hour and a half session. She also handles all referrals for me for other related appointments and makes arrangements between patients and former patients for support when she is not available.
Endocrinologists and hormone replacement therapy. I wouldn't even bring this up to your folks. You have oceans of time before this becomes a problem and confronting them with it now will most likely be met with a stone wall defense. Once you are an adult then you can seek it out and well afford it on your own.
Surgery- don't even worry about it right now. Focus on the things that you can do now like voice therapy, pose and motion, diet/exercise and learning the basics of make up. It sounds like "too little and will be too late" but it's not and a lot will change by the time you secure your education at a university or tech school. Remember we often have issues with money so don't let your skills lapse and protect your credit rating.
Support- look around or google for some LGBT or especially transgender support groups. CATS in Charleston was a great help to getting me started.
Tips and feel good junk food TV- many of our members here have these little YouTube logos under their avatars. They often have a series of videos that you can watch with stories about their transitions. We all have our favorites.
Reading- lots to do here and I'm sure that many of our members can recommend some good books on the subject. I read "Warrior Princess" the Kristen Beck story when I started down this path. It really made me feel normal amongst all my anxiety about being transgender and how wrong that felt.
Well really that's enough from me for now. Start asking more questions. We have answers from different perspectives and we come from a variety of different back grounds and career experience.