What can you as the parent actually afford without taking parent loans or cosigning student loans?
What were the previous promises and understandings you had with both kids about college funding? What about fairness in college funding – if your pre-med kid chooses cheap compared to the other one, will you offer the money not spent on undergraduate toward (expensive) medical or other professional school costs if he goes?
Remember also that medical schools may not be too enthusiastic about very young medical school applicants, particularly those who took most of the pre-med courses at community colleges (although taking upper level biology courses may somewhat mitigate that situation, he may want to take additional higher level chemistry, physics, and math as well). All medical schools are highly selective, and most pre-meds do not get into any medical school.
Remember also that biology does not have very well paid job prospects at the BA/BS level if he does not go to medical or other professional school.