This February article in U.S. News & World Report hit the nail on the head with the very first paragraph:
"Can you afford to go back to work? The extra family income sounds great, but many women returning to the workforce forget to account for a lot of expenses. The truth is that working costs money, from child-care expenses to dry-cleaning bills to maybe even hiring a dog walker."
The article goes on to list several issues (childcare, commuting, etc.) that women need to consider before opting back in to the workforce -- as well as the average costs associated with each issue. Worth a read if you're wondering whether working out of the home is worth it for you and your family.