https://www.nytimes.com/2019/11/25/health/medical-school-cost-diversity.html
Article describes the financial struggles that medical students from low SES backgrounds face (in both pre-med and medical school).
It also links to https://www.aamc.org/system/files/reports/1/october2018anupdatedlookattheeconomicdiversityofu.s.medicalstud.pdf , which shows that just over half of medical students come from families in the top 20% of income (and nearly half of those come from families in the top 5% of income).