How to get a diagnosis? (Preferably that I could afford and have without my parents being involved)

I’m not diagnosed with autism, my parents believe I have it, and I have shown signs through the years of having it, however, my parents don’t want me taking the assessment because they don’t want me labeled. My argument to this is that if I have it I would be able to accommodate for it, they still don’t exactly care.

Right now, my plan is to try and get the assessment when I’m 18 and moved out, since they said they’re fine with me doing that since I’d be an adult, however, I have heard that people who try and get the assessment that are older are less likely to get a diagnosis even if they have it just because of the assessors and stuff.

My question is:

Should I try and ask them more for that assessment? (I know if I push hard enough they’ll let me get it)

Or

Is there anyway to get an assessment online or without insurance?

Or

Would I just be fine waiting until I’m 18?

Either way, I’ll be fine with or without the diagnosis, I’d rather know I don’t have it than have it and not know.

Any advice is welcome!