A., you've received some very good information and advice. One mother mentioned WIC. If you're eligible for WIC they will also provide vouchers for nutritious food for you while you're pregnant and then for both of you after your baby is born.
I would add that even tho you feel like you know all that you need to know you will discover that isn't so. Mothering does not come naturally. Loving and wanting to mother is a natural feeling but you will discover once the baby gets here that he/she is much more complicated being than the idea of baby is.
If you will have your mother, a sister who has given birth, or a close friend with experience then you will be more comfortable. At the same time not only is the world more complicated so is the care of babies. For example both my mother and my daughter have inverted nipples. My mother was told she couldn't breast feed. My daughter was given shields and training in how to use them and she was able to breast feed. The class will bring you up to date on several things that could happen and how you can manage them.
I'm curious about your statement, "so called birthing classes" If I'm interpreting this correctly, that you're putting the emphasis on birthing and we all know giving birth is natural and women for years have been doing it without classes I'd like to add a couple of things. Not all births are "normal or natural." In the old days when women gave birth at home without assistance many babies and mothers died. This class not only gives you information about a "normal" birth and teaches you how to manage pain and ways to have a more comfortable birth, it will also tell you about events that don't fit in that norm so that, if they happen to you, you can recognize them and feel more comfortable about whether or not you need to do something about them and if so what.
I've been at two births during which the mother had an epidural. They still were actively involved in the birth and they were still uncomfortable. Their husbands would remind them of ways that they'd learned to relax and get in a more comfortable position. While you're giving birth you will have difficulty coaching yourself.
The birth will be somewhat easier if you've been doing prenatal exercises to strengthen your muscles and are in good physical shape.
And as several have mentioned, you will be better able to plan for the type of birthing experience you want. You will also be more comfortable during the birth because you will know what is happening.
When you get that baby home you will discover that you either don't know what to do at times or you will feel anxious because you're not sure that you did the right thing. While before you felt confident, once the baby is home and you and your husband are alone the full weight of responsibility for this tiny helpless baby will be on your shoulders.
Birthing classes provide much more than info on birthing. They include the time leading up to giving birth and about your body after birth as well as info about your new baby. My daughter liked the birthing class because she could talk with other women about what was happening with her body. They comiserated together.