I don't want to sound pessimistic, but starting your HRT on pellets, when just out of high school and not thinking your parents will help... "2228.57-3342.86 $ a year. Not counting eventual antiandrogen pellets." is what I roughly calculated from Jennygirl's numbers before. I don't see anyone who's just starting out in life, unless very well off or helped by caring and rich parents, being able to get those. :/ Especially since at this point other costs of transition are likely to be weighing on you.
As for your parents... I don't know your situation, really, but I should say that so far, the vast majority of trans people being afraid or even convinced they would be kicked out by their parents if they came out, that I've read about, found that things went better than expected. Some were bracing themselves for expulsion but were confusingly greeted with support. Less extreme cases were brazing themselves for inacceptance only to find folks who needed some explanation and convincing before they understood.
On top, I was amazed when I read about the story of a (then) young trans woman who transitioned in the 1970s, whose parents didn't accept at all, and they were ashamed of "him". Yet those parents had the decency to wait until she was done with high school to disown her, and when they did, they provided her with some very minimal monthly survival funds so long as she didn't come close enough to them to embarrass them. I was like "whoa, even parents from another age who really didn't understand or support didn't completely abandon her."
I'm not saying there's no risk, and heck, for all I know, things could go anywhere from awesome to awful to you. Just, well, consider this and how many others wished they'd told their family sooner, and weigh it with the perceived risk. I may be being overoptimistic about that though, since I've amazingly been accepted at least decently by everyone so far, but I still do have a feeling that the risk is often much lower than feared.
Jennygirl: I'm curious... Repeatedly having those mini-surgeries... isn't it annoying? Or rather painful? And uh, does it leave you scars? Also... do those pellet things poke through the skin? I still don't have the money at all (and whoa, when I think of it, actually, if I did, I could affort so much electrolysis, or maybe even a tracheal shave in two years o.o).