Mike McDerment discusses metrics for determining how much a company should spend to acquire new customers, including: - Cost Per Acquisition (CPA) which is marketing spend divided by the number of new paying customers acquired to determine how much is spent per customer. - He outlines three approaches to evaluating CPA based on the company's stage: CPA compared to ARPU for early startups, CPA as a percentage of Lifetime Value for larger companies, and CAC Ratio for more established companies spending on marketing for 6+ months. - The goal is to balance growth objectives with available cash resources by keeping CPA ratios such as CPA to ARPU, CPA to LTV, and