Interpreting "likely to pay" survey results

I previously posted about adding a survey to my site to see if people would be willing to pay for a premium version.

Take up on that survey has been quite low - only about 0.1% of my visitors have answered and I currently have a whopping 11 results.

Of those 11, 25% say they are willing to pay. I need to convert 0.1% of my monthly visitors (30k per month, so 30 sales per month @ 0.1% conversion) into paying customers.

Obviously 25% of my 11 respondents is not a fair sample. I am wondering, however, if I am ever going to derive any useful information from this at all. Even if I end up with 100 responses, it's still such a low portion of my users. I reckon those who answer a survey are more likely to buy in the first place; they're the more engaged users.

How do I interpret this data? At this rate I'll need to run the survey for months and months to get even 100 responses.