Is there any cheap ways (Under $300 dollars) to have the security of an ERC-20 token smart contract checked? Thank you to anyone who can help.
Are you implementing Openzeppelin's contract or creating your own, if yes and you're not writing any custom methods, then you can write your tests and do some slither or MythX analysis by yourself. Openzeppelin's contracts have been audited so you're protected.
However, if you have some complex activities you're performing outside the standard specifications, you might need to employ an external auditor. However, Secureum is running an audit course, you might want to reach out to the person in charge, Rajeev, as he can maybe share your contract with the cohort members and get them to audit it for you. You can also join Kernel's Audit track and get your contract analysis done there.
NOTE: For critical projects, you'll do well to increase your budget and submit your contracts for Audits with a very good auditing firm like Consensys Diligence, Trail of bits e.t.c.