Gary, don't be bothered by everyone's offense at your question. There are a few things that seem to make people unwilling to talk reasonably around here, and kids is one of them. I definitely agree with ex-Jarhead's short answer "it costs plenty." Estimates range from $100-500k depending on a lot of factors, and any individual's experience may be far outside that range (Amy Daczyczyn or Paris Hilton).
When you look at the people on this board you see more childless couples than the general population (though that's just a guess, and I haven't tried to quantify it), and few people with lots of kids (though people with lots of kids are rare in our society these days). Several people have mentioned limiting the number of children as a route to easier early retirement, and the famous early retirees Terhorst and Dominguez were explicit that being childless made the path easier.
Is having a child worth it? I made the decision to have children with my eyes wide open to the fact that it would cost a great deal of time, effort, and money (with not a small amount of coaxing from DW), so I certainly think so. You have to decide for yourself what you want to accomplish during your short stay on this planet. I decided that having children was worth whatever it might take.
Finally I suggest also that those of us who are true savers, those who plan far far ahead, should not forget the big payoff for having children -- grandchildren.