Women who have a good health insurance policy may have all their prenatal care covered. In this case, you may well be limited in your choice of prenatal care provider by your insurance company. Some insurance policies cover prenatal care in part, and may leave out some specific tests like amniocentesis (which can be seen as optional). In the United States, even an uncomplicated vaginal delivery in hospital can cost around $8000. You will have to check how much of that would be covered by insurance.
Pregnant women who are not insured may have the option to join a government insurance program such as Medicaid. It is also sometimes possible to get prenatal care through crisis centers. If you have specific wishes, like a homebirth midwife, this is unlikely to be covered by such programs. Homebirth midwives tend to cost between $2000 and $4000 in the US, a fee that usually includes the delivery as well. But again, this varies depending on where you live and should be checked. Optional diagnostic and screening tests, like an amniocentesis or a 4D ultrasound, may be paid for by insurance, or may have to be paid out of pocket.
Couples who are trying to get pregnant are wise to check all the relevant details with their insurance before conceiving. If you are uninsured, now is a good time to look into different insurance options. It may not be possible, or very difficult, to take out a new insurance policy that covers maternity care while you are already pregnant.