Is it possible not to have spent any money on paid advertising at all? Do you think these are the result of word-of-mouth, or very good content marketing?
David brings up a great point. You are INVESTING in something -- relationships, great design, strategy, content, etc...
There is no such thing as a 'FREE' customer. You have to spend money to land that customer. You might spend that money on advertising or on a better content marketing team.
Don't expect big results with little investment. It's going to cost you.