Who really has the cheapest car insurance?

"I'm a stay-at-home mom (in Arizona) and I want to get medical  insurance . My boyfriend (and our baby) have  insurance    through his company however it's like $400/month just for the 2 of these and it doesn't cover considerably. To include me to his strategy we'd have to get married plus it would be over $200/month significantly more than he is currently spending now