I think electing to enroll in a less prestigious medical school when you have the opportunity to train at a very highly regarded school AND paying $100k more to go there without a really compelling reason is a colossal mistake.
WRT prestige, it's certainly less important than USMLE scores, LORs, and interviews, but when the difference between residency applicants at top programs is razor thin, it certainly could make the difference between getting your 1st choice or not. I interview residents for a very competitive fellowship. I can't say I put a lot of weight on their medical school, but I do consider the perceived strength of their residency, especially if we've had outstanding fellows from there before. Maybe that's the difference between calling you a 9 vs 10/10, and getting in or not.
If I were you, I absolutely would want all the edge I could get, and the extra $200k (interest) in my pocket. That's at least a third of a nice home in most of America. (Perhaps more important than ever as future salaries, etc are less and less certain.)