Affiliate Marketing Secrets

I am looking for a legitimate way to supplement my income to afford college tuition and groceries and rent. All I can find are scams and sites where they want $47-97 to join then want me buy extras. Upon research I have found that a vast majority are just scams.
Are there any good ways to make a decent living, at least a part-time job worth of pay? Besides selling on eBay, I already have made any money I can from it and it wasn’t enough.
Is there any ways I can legitimately earn money online with out huge start up costs or a month of training? I need the money fast, however I don’t need to earn over a thousand dollars a week. My primary job at a Kroger has cut my hours to part-time and I never know whether I work days or evenings so I have been unable to find a second job. I am just looking for an extra $300-500 a week.
Please don’t reply with any scams. Feel free to use affiliate links, however, know that I will be doing very in depth research on any products posted.
Thanks.