TEENage chest binder help? (& what will I as a trans kid in high school?)

I’m a 13 year old who wants to buy a chest binder for myself. What are some good websites to buy a cheap chest binder for my small teen bod? I need a cheap one because I’ll probably grow out of it and I don’t have much spending money, but I want a binder that won’t strangle me or give me burns, bruises, or rashes. 
Also, I thought that waiting until I grow more wasn’t an option because I should probably start wearing chest binders before I go into my first year of high school, so people in my high school don’t know i have breasts. The only problem with that is that I’m a femme-ish agender(?) kid who has never been in the boy’s bathroom, and I don’t really want to change in either the boys’ or girls’ locker rooms. I live in California, in an area where LGBP people are respected, so I’m guessing that if people DO know that I’m trans it won’t be that hard for me, and I’ll only be verbally harassed sometimes (and maybe teachers might try to make me fail). Now I’m not even sure if I should wear a binder in high school.
Any advice?