There are too many factors that go into this decision to say that it is simply a money one...
I have covered the gammit on this one...stayed home full time w/ first child (HATED it...not my personality, plus DS1 was high maintenance kid--and still is!); worked part-time w/ #2--LOVED this. Got my adult "fix", with plenty of time for the family; with surprise #3, I owned a retail business. I was back at work (after a C-section!) TEN DAYS after his birth--with him in tow! A year later when 9/11 occured, I was worried about making the bills at home & the business...I went back to teaching full-time AND still had the business! (yes, the next 15 months were insanity until we closed the store!!!!)
I am blessed. I teach full-time (home ill today

no worries, teacher work day anyway), and am able to take my youngest 2 to the school that I teach at. It does mean that they are with me the hour before school starts (officially, only 30 min. of "work" time...my principal has been supportive; heightened level of conern around here as we get a new principal for next year...hopefully it will all work out!). But a teacher's schedule allows me the best of both worlds...I get my adult time, money for travel & extras, but still plenty of vaca time w/ kids (we are addicted to golf & the pool in the summer).
THE KEY IS THAT YOU ARE HAPPY WITH YOUR DECISION. (no, not every minute of everyday.....

) Hope for the best, plan for the worst (in other words, if you are a SAHM, BE SURE you have sufficient disability & life insurance on DH, AND keep your job skills up to date).
My mother stayed home w/ us for a few years when we were young, and speaks of the same concerns I had when I was a SAHM...if an extra bill comes up HOW are we gonna make it??!! My mom ended up nursing at night, so she could be home if we were ill, and pick us up each day after school. But it was a sacrifice...she was one tired crabby lady most of the time (can you blame her??!!)
Again, as long as you are happy--yes, YOU, not just DH--all will work out. My children were in daycare full or part-time for most of their childhood. (and we were SO lucky...almost all inhome care, both former elementary teachers, one a dear friend--both SO GOOD) And they truly are wonderful children. Bright, well-mannered, and they have rarely been ill (oh, I didn't breast-feed, either---it just didn't work out, though I tried with first 2--sorry, just always hear how those formula fed kids are more sick. Sorry, just not true. Breast feeding is great, just not the only way to do it well....I'll get off my soapbox now...)
WELL...I digress....to wrap this novel up...as my mother said, "Being a mom is your greatest joy...and your greatest nightmare all rolled up in one." Yep, she nailed it. And this is true whether you are a SAHM, WAHM, WOHM...WHATEVER. Being a mom is hard work, but the rewards are great!