$90,000 in debt for an undergraduate education is a bad idea. The best-case scenario (absent a fairy godmother to pay off your loans) is that you graduate from Chicago at 22, and complete a MD/PhD program at no cost in 6 years (7-8 is far more common - 6 is the near-absolute minimum). You’ll start earning real money in your late 20s, after a decade of interest payments and/or principal payments on your UG debt. $27,000 in Stafford loans will cost you $49,000 including interest (assuming a 20-year loan term, since you won’t have the income as a med student to make a 10-year repayment plan feasible). You’ll also need $63,000 in PLUS loans, over a long term, and once interest is factored in those will cost you north of $130,000. I ran these figures using the calculator at http://www.finaid.org/calculators/loanpayments.phtml.
In short, you’re looking at $180,000 in loan payments. That’s $750 and change each month for 20 years, including a decade when your earning power will be limited by the fact you’ll still be a student. Those are the figures you need to bear in mind.
Make sure, also, that you aren’t extrapolating UChicago’s current COA over 4 years to arrive at the $90,000 figure. Annual tuition increases could easily add $10,000 to the 4-year COA, which would push your debt to $100,000 and total repayments to $200,000. If you’re a heart surgeon at the Mayo Clinic, $200,000 may not be a huge burden. If you find a job that doesn’t pay a top-2% or top 3% salary - or if your MD plans change - that debt will limit your options in life for a long time.
For some perspective, you could attend UChicago rather than another excellent school for your major, or you attend UW and buy a 3-bedroom house with the savings.