1. First, is the cost of child care. Child care costs are very expensive.
The average cost of center-based daycare in the United States is $11,666 per year($972 a month), but prices range from $3,582 to $18,773 a year ($300 to $1,564 monthly), according to the National Association of Child Care Resource & Referral Agencies (NACCRRA).
2. When you stay at home, your food costs are much lower. You won't need nearly as much convenience foods and stretching the budget is much easier.
3. You won't have as much expense for automobile costs as you will be driving less and, if your circumstances allowed, could possibly even get buy with one less car.
4. You won't need to spend as much on clothing. Plus you will have time to shop at thrift stores vs just running in and out of stores buying what you need as fast as you can.
5. You will pay less in taxes. This is a real cost when you consider hourly pay.
6. You will have more time for thinking of how to be more frugal in every area of your life.
7. You may find yourself feeling content with less since the friends you have will have more of the same frugal mindset than dual income couples.
8. You may be able to come up with a way to create income from home.
Here is a stay at home calculator. (I haven't personally used this but there are many such calculators online and you can find one to fit your needs!) http://www.parents.com/pregnancy/considering-baby/financing-family/calculator/ Using this, you should be able to calculate whether you can afford to quit your job or not.
For me personally, I felt I couldn't afford to not stay home with my children. It was something I deeply wanted to do. Having done so, I learned to be very frugal. It was such that, after my children were older, (and since I wasn't paid a huge hourly wage!) that working more than 20 hours per week actually cut into what I was able to make, because after 20 hours, I wasn't able to be as frugal as before because my time was spent at the job rather than doing frugal things.
This is a very personal decision for every couple, but I think you would be surprised at how much it actually costs you to work and that you just might be able to quit and make it much more easily than you thought!