Got married to someone who thinks like I do wrt to retirement and with one child we are on track to 'retire' when we want to. Barring us doing something dumb or global financial meltdowns - by mid 50s or so. I put retire in quotes because who believe in retirement where one site on their ass all day and says I'm so glad I don't have to work any more? I don't. Retirement means we will be able to give meaningful time to .org's that need it. But this will still be 'work'. I can't imagine a worse hell than retirement where I have no meaningful work to do.
Note: with two or more children much of what I can still do would need to be re-evaluated.
The cost is over a $1,000,000 (with a Dr. Evil pinky). If you look at the costs online, then you will see something between $200K to $400K depending on how good of parent are you. However, this doesn't bring in the opportunity cost of investing. If you just take the 18 year time span, then the first year is insanely expensive. Now, imagine it expanding 30, 40, 50 years out.