Around 50 bucks for off-the-shelf, 200 for custom.
You are asking all the right questions for a newbie, and so young. Kudos!
The one thing you need to keep in mind is that boot-fitting is incredibly technical. And so is this sport in general. Please stay away from "big-box" stores. I started skiing 4 years ago and I started off in a big-box place. I wasted 650 bucks on a boot fitted by a completely inexperienced kid. I had to buy again soon. Total waste. Rentals there would be terrible.
When you get to a real ski shop, even if for season rentals, you will see the difference. These people ski all the time, they take courses for boot-fitting, and know so much about your foot, what it needs, etc. Things like shin alignment, canting, etc. It's a whole world.
So, my humble suggestion is that once you have an overall plan, you ask here for suggestions for good places. We all do when we get to a new area, etc.