Business School is SO NOT NECESSARY!
Business school is for those who want to work for other people, NOT most entrepreneurs. My argument is that NO BILLIONAIRE startup founders ever went back to school to learn how to run their company. They learned through mentoring, reading and doing.
You can do the same.
Find a successful business person and ask for them to meet with you once per month for lunch where you come loaded with questions. Successful people normally love to share their knowledge with aspiring people.