OK, good question. I may be able to develop a fuller response after a bit, but what you are doing is setting up one model where you just create a special expenditure(s) called "college costs" or something and enter all those costs as they would come out of your own economy (i.e. regular assets). If you had a 529 setup, that would be a little different. But using special expenditures as non-deductable (if I'm thinking right) expenditures. Then, in the other model you look at a particular loan and using the term of the loan (or an online amortization calculator) to find the stream of payback on that loan in annual terms and enter as special expenditures those annual payments (presumably starting in a future year) for the years it takes to pay back the loan. The interest on that loan will be implicit in your amount you pay back each year.

When you are modeling this using your own money, I wouldn't count the money that belongs to the student. In other words, say Jack has saved $2000 for this expense and is willing to ante up that much and you pay the other $20,000. So you'd enter your expenses as $20,000 not $22,000 since I presume that you don't have his $2K in hand now. In other words, I'd view his contribution as a way of lowering your cost.

I can have others look at this too. Perhaps there are other strategies. But is that what you were thinking?

Well, that was sort of where I was going with my thinking. Yes, the student's household economy is really something different from the parents--different taxes, different income, expenses, social security, etc. So supporting a child is no different from any other kind of special expenditure in that it's an expense on your economy and you can model the tax consequences (and interest costs in the case of a loan) on that expense. From the child's point of view with her own family profile, it's a similar situation except the impact is on her profile, not yours.