From the Federal Elections Commission:
https://www.fec.gov/updates/statistical-summary-24-month-campaign-activity-2019-2020-election-cycle/
“Presidential candidates raised and spent $4.1 billion in the 24 months of the 2019-2020 election cycle, according to campaign finance reports filed with the Federal Election Commission that cover activity from January 1, 2019 through December 31, 2020.”
So, while $100mm seems like a lot to you and me, it’s small potatoes for a Presidential campaign.
Yes running for a job that pays what 200k but it’s the power they are buying.