What would you give for filling out a survey?


As the title says, what would you give someone for filling out a survey.
I am going to design a very short survey (for research purpose), the most will
be 3 questions relating to web design & am going to send it out to small businesses.
What would you give as a ‘thank you’ for filling out the survey?
I am not a very big company just a lone person with not much of a budget.
Any sugesstions greatly appreciated.