Email me when we cross $X amount in one day, Text when we cross $Y, and Call when we cross $Z. Additionally, allow the user to configure a hard cut-off limit if they desire.
Just provide the mechanisms and allow users to make the call. Google et al would have a much stronger leg to stand on when enforcing delinquent account collections if they provided these mechanisms and the user chose to ignore them.
Additionally, Google et al should protect _themselves_ by tracking usage patterns, and reaching out to customers that grossly surpass the average billable amount - just like OP with their near $100k bill in 1 day. Zero vetting to even have a reasonable guarantee the individual or company is even capable of paying such a large bill.
And then what? Sue a company that doesn't have $100k for $100k? This makes zero sense.