i personally average around $100-150 per month on surveys. sometimes it's less...but the thing is, the more sites you register with & the more time you put into it, the more likely the focus group offers will come your way (they are infrequent). Those boost your numbers up nicely
...just last monday i pulled in $165 from a focus group which lasted 1 hr. I have another one this thursday that's paying $100.
bottom line, if you want to rake in any decent amount, you have to sign up for a bunch of sites, and devote some free time to it every day.
if anysite ask for money. 
