Online only? Because with $500 I'd flip things, that's at least little risk as worst case scenario you buy $500 worth of stuff and (probably) sell it for $500. Unless you're a massive idiot, which I don't think you are, then it gets pretty hard to lose money while flipping. It's also hard to make money sometimes, but it's little risk.
If you want online only that makes it harder. Your competition goes through the roof as anyone with a computer, and $500, could compete with you. If that's the case, you really got to figure out what YOU want to do. There's no point in me going "yeah, you can make money with porn." if you don't like porn; but there's also little reason for me to run a food blog if I hate cooking.
IMO online only, it's absolutely critical... CRITICAL... that you love the work. Online is easy to slack off, you're online so one click and bam there's games and Facebook. Online has lots of competition. So you really have to enjoy the work or nothing will get done. People think online is easy, only if you love the work, if you don't... it'll be one of the hardest things you've ever tried to do.