Final answer:
A startup company can set up an AWS billing alarm to receive notifications when their monthly AWS bill exceeds $2000, which is the most immediate and cost-effective solution.
Step-by-step explanation:
The option to notify a startup company when their monthly AWS bill exceeds $2000 is to set up a billing alarm in AWS. This function is provided by the AWS Billing and Cost Management dashboard, where you can create a billing alarm to send a notification when costs exceed a certain threshold. You would use Amazon CloudWatch to define the alarm and then set it to notify you via email or SMS through Amazon Simple Notification Service (SNS) once the specified $2000 limit is reached. While manually monitoring or using a third-party cost management tool are possible, they may not be as immediate or may incur extra costs. Contacting AWS support would not be efficient as AWS provides tools to automate this process.