Blood test for gender?

I have my first appointment at 8w5d (next month.) I am a teacher, and from what my coworkers have said, a blood test to determine gender is not covered in treatment with our insurance. Is this something optional you can ask for? How much does it usually cost? I don't want to ask about it at my appointment if it isn't common for people to do that, but it's my first and I would love to know the gender. I told a friend I was considering buying one of the sneak peak tests, but she said that was something silly to spend money on and I should just wait.