Im sure most android users know about this but Google released an app a while ago that lets you do short surveys in return for credit on the Google Play Store.
For instance a survey I recieved today had two questions
Q: How many hours a week do you drive
1 : 0
Q: What would you like to be made easier whilst driving on your smartphone
4: can't remember
5: Other (Free form text box)
This survey got me 26p which I know isn't a lot but it took 20 seconds to complete so with enough you'll be able to afford some premium apps. The app itself is free and is worth trying as it won't take up too much time