The "opportunity cost" of having my dd was quite high, since I quit my job to stay home with her. That's the lost-salary cost. But even though I use disposable diapers, she hasn't cost anywhere NEAR $700/month. I breastfeed, of course, and even once she started solids she wasn't a big fan of the baby food that comes in little jars, so we just gave her food off our plates (oh, and graham crackers ... those were her first solid, since she didn't like eating off a spoon). We got a whole lot of hand-me-down clothing, and a hand-me-down crib that we never use (though now we do have the mattress on our bedroom floor, and we use that, so it's nice to have it). And a hand-me-down changing table and bouncy seat. Now that we don't get hand-me-down clothing any more (dd at 16 months is now TALLER than the 2-year-old we were getting those hand-me-downs from...) I buy her stuff new at Target. I got her two pairs of PJs a couple weeks ago for $6 each. As everyone here has aptly noted, raising a baby is not expensive; living up to society's expectations, THAT'S what's expensive. (We don't have a "Classic Pooh" nursery because before we can decorate, I'd have to clear out all the junk we store in that room
We didn't have electronic dollies back when I was a kid, but I did have a middle school teacher who made us all carry eggs around for a week. I don't remember what I did with my egg, but I think I carefully carried it home and then left it in a box on my dresser, with the emphatic approval of my own mother, who thought the whole assignment was ridiculous. "An egg is NOTHING like a baby. Babies RESPOND to you. Babies are INTERESTING." I attempted to argue this point with my (childless) seventh-grade teacher, who insisted that a newborn was every bit as unresponsive as an egg.
I found myself thinking about this when dd was about a month old. My mother was right (of course); a baby is NOTHING like an egg. For one thing, even a newborn baby is less fragile than an egg: while you don't want to drop one, you can hold a baby quite firmly and she's not going to break in half in your hands. But more importantly, a newborn is soft and warm and yielding, and, yes, RESPONSIVE, right from the beginning. (They have to be. It's a survival-of-the-species thing.)
The thing that strikes me as SAD about those scare-tactic anti-teen-pregnancy campaigns is that it's not as if the essential message, "CHILDREN ARE A HORRIBLE BURDEN TO BE AVOIDED AT ALL COSTS," goes away when the recipients of the message turn 22. No, those messages lurk in the back of your mind, convincing many young women to postpone childbearing for a long, long time, because they "know" it's such a horrible burden to have a child, and they don't think they can possibly live up to the responsibility. Worse, I think that fear of the "burden" of parenthood fuels the demand for books and systems that promise to make the whole thing easy -- like, oh, "Babywise."
Of course, having children DOES profoundly change your life. You probably will not to go out as much once you have your baby: dh and I have cut back on going to the theater, on eating out, on movies. We still do stuff like that occasionally, but we have to plan in advance, arrange a sitter, etc. But the tradeoffs, compared to the rewards, seem to small to me now. I think that's true for most parents.
I'm a writer (my first novel, "Fires of the Faithful," is coming out in October from Bantam) and I'm in a writing critique group with six other people, one of whom is also a parent (and one of whom has a pregnant partners, so is going to be a parent in another few months). One of the childless men in the group talked to me once about parenthood and how much it cut into writing time. I assured him that it IS possible to write with a child in the house, though you do need to be flexible about when you write. And I told him that no matter how much it cuts into your writing time, honestly, kids are WORTH it. I'm not sure I convinced him, though...