How do I compete with bigger brands' ad budgets?

As a small e-commerce business, I'm struggling to compete with larger brands that have massive advertising budgets. Every time I try to run ads on platforms like Facebook or Google, I get outbid and my customer acquisition costs are skyrocketing. I need strategic approaches to maximize my limited marketing budget and find ways to effectively reach and convert customers without burning through all my resources. How can I create a competitive marketing strategy that allows me to punch above my weight class?