How to make extra money online?

I'm a school crossing guard making $10 an hour. I work 10 hours a week. The pay isn't bad but I want to earn extra cash on the side. I'd prefer something I can do online as I could do it in between my shifts. Also it has to pay relatively well. I'm not looking to get rich quick but I would like to earn a decent amount if possible as I will not be working during the summer. As far as start up costs, I'd prefer to not have one but if there is, it must be really low (ie: $5-$10). Thanks in advance