Should I invest in paid tools or use free alternatives?

As an e-commerce business owner, I'm constantly weighing the pros and cons of investing in paid marketing and optimization tools versus using free alternatives. My budget is limited, and I want to make sure I'm getting the maximum value for every dollar spent. I've seen numerous free tools that seem promising, but I'm concerned about their limitations. How do I determine whether investing in paid tools will actually provide a meaningful return on investment, and what criteria should I use to make this decision?