If the sites are asking you to pay to join, they are a scam. Legit sites never ask the users for money.
This is the best review of online paid survey sites on the web. I found this site and this is how I got started with these kind of sites.
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The sites are reviewed and the best available are suggested to readers. They also describe payment options for the survey sites. They won't make you rich but they are good for few extra bucks a month depending on the site.