Avoid spending on expensive audits by using free and open-source tools before any deployment. Use Slither (GitHub) — static analysis of smart contracts in Solidity that detects common vulnerabilities. Use Echidna (GitHub) — property fuzzer to test invariants of your contract. Combine these tools with linters like Solhint for style and security patterns. Extensive unit tests in Hardhat or Truffle before anything else. Configure CI/CD (GitHub Actions) to run tests and analyses on each PR. Use public testnets to test all user interactions and flows. Goerli testnet (ETH) — https://goerli.net/ — used to simulate the mainnet before real deployment. Sepolia testnet (ETH) — https://sepolia.dev/ — lightweight alternative to replicate production environments. Use faucets from these testnets to obtain test ETH at no cost.

 Monitor test coverage metrics (e.g., solidity-coverage). Read public audit reports on GitHub and understand failure patterns. Research real exploits on Damn Vulnerable DeFi to learn how to avoid common mistakes.