I'm not projecting costs in a systematic way, because there are too many variables and my kids are age 6 & 3. I have two kids, so the basic options are:
1. Neither of them go to college, expense=$0 (highly unlikely in our extremely privileged and educated family)
2. One goes to college, one does not go or gets full ride, expense= at least $200k by the time they get there, possibly more
3. Both go to private or public colleges, expense = at least $200k, probably a lot more
With our assets I don't feel good about taking financial aid from others who truly need it, so we will save at least $200k in 529 plan, maybe up to $300k depending on what the outlook is like as we get closer to RE. The rest we will figure out as we get there. Multiple choices for covering the rest of the cost, including taxable accounts, loans, kid getting a job, living at home for a year to save, choosing cheaper college if our finances really tank. In other words, flexibility is key, once you determine how you want to prioritize the covering of that expense versus quitting your job.
Important side note for those who question the value of paying for a child's college: both my parents and DH's parents paid a substantial portion of our private college tuition, and room & board for the first two year. After that we both covered our own room & board, and I graduated with loans as well. The assistance from parents was very helpful, but we also learned to work hard and pay some of our way.