Studying where your competitors' links come from, without any paid tools, still gives you a reasonable sense of the kind of sites worth pursuing in your own outreach.
Look at Their Press Mentions and Partnerships
Publicly visible coverage and partnerships often reveal real, findable link sources you can pursue too.
Note Patterns Across Multiple Competitors
A type of site or content that consistently earns links across several competitors signals a reliable pattern worth understanding.
Use Findings to Shape Your Own Outreach List
Competitor research is most useful as a direct input into your own realistic list of link targets, not just an interesting observation.
Next step: Use the SEO Audit to compare your own site's current authority against your competitors before planning outreach.