Depends on which program you're interested in.
QR-there is the Site of the day, Clicks, Paid Emails, trivia surveys all don't require any money.
Swagbucks-there are multiple ways to get codes, but you have to be fast sometimes. I use it to search and occasionally get points that way.
Freeride-very slow earner-surveys and grab a cab
there are survey sites like mindfield, zoompoints, etc that pay in points and then get checks,
amazon gift cards, etc
If money is tight, have you thought abut couponing? If you do it right, it will definitely help stretch a dollar.