Right now I am situated the best I ever had been, since I had my oldest 12 years ago. I work from home with a flexible schedule, so no daycare costs. I wake up to work 2 hours before my kids and stay up 3 hours after they go to bed. When they have activities, I bring my laptop and find a private, quiet corner to work until the activity/practice is over. Monday is the only day they don't have activities so I've instituted "movie mondays" this summer and they aren't allowed to bother me while the movie is playing so that I can retreat to the master bedroom/office and work. It's exhausting, trying to squeeze work in every spare child-free moment of my day, but cheap. My 4 year old is going to preschool this year, that will only cost $150/month for 2 1/2 hours per day, M-F and of course I'll use that time to work, maybe I won't have to stay up so late.
A big cost of work that's been bugging me is the extra expenses. Of course, I don't have to spend money on a work wardrobe now that i work from home, but I don't have the time to do all the money-saving things that i did as a SAHM. I know, I know, boo hoo, poor me--I want you to know that I'm not really complaining, just sharing.
I belonged to a homeschool preschool co-op, so that saved us $150 a month.
We participated in two playgroups and I traded favors with all the moms so I almost never had to pay a sitter to watch my kids. I think all of us parents know how valuable that can be.
I had time to make extravagant home cooked meals completely from scratch, and comparison shop and coupon for the best prices on groceries and toiletries. Now, I pay a bit more to buy convenience foods like frozen veggies, I don't have the time to pick and can my own produce, I have to buy jarred spaghetti sauce, we went from never eating out or getting takeout to doing it at least once a week.
I used to bake my own bread, bake treats for my kids and husband every day, make homemade ice cream and plan elaborate family nights, complete with personalized menus and coordinating craft projects and games (I hunted down a huge box and made a "box of shame" for Despicable Me movie night, I created a 6 hole mini golf course in our backyard complete with flamingo covers for the golf clubs, created by cutting and gluing craft foam sheets for our Alice in Wonderland night, I could go on but I think you get the idea).
I did my best to be super mom, and now I feel guilty for not doing those magical things for my kids, but if I do take the time to do similar stuff I feel guilty for not working--I'll find myself thinking, "if I had spent this time working I could have made 'X' amount of dollars". It's terribly hard for me to separate work from home life now that I work from home, it's like I'm at work 24/7. Oh, and over the last year I've been working from home i've managed to back out of most of my volunteer commitments : (
So to sum up, for me the biggest cost of working is the guilt. This isn't the first time I've worked, though I have spent more of my adult life as a SAHM than as a working mom. Even when I worked outside the home I struggled with the mommy guilt. And the wife guilt, I don't do nearly as much for my husband as I used to--in fact, when he woke up today he couldn't find any boxers in his drawer. I thought I was keeping up with the laundry for everyone equally, though we always have dirty clothes in the hampers, but it turns out I was mostly washing clothes for me and the kids and neglecting my husband's hamper. More guilty feelings.