What is your customer acquisition cost?
patio11: It depends.I get the majority of my customers through organic SEO.  The marginal cost of a customer from organic SEO is zero.  The amortized cost is almost impossible to calculate -- I SEO well because I spent years learning the technical/marketing aspects and, e.g., blogging (which has a side effect of getting me domain trust), writing useful resources for my niche, coming up with a content creation strategy, etc.  (The great thing about content creation is that if you're making evergreen content you pay for it once and then it keeps getting you customers/links/etc for forever.)AdWords, on the other hand, is pretty easy to calculate marginal CPAs for.  My previous experience with Google leads me to believe they understate my conversions with them, but just reading the number off the AdWords report, I spend about $12.25 per customer.  Since I make about $29 from each customer after all costs but advertising, I'm quite willing to do this all day long.For those of you who are more interested in cost per signup rather than cost per paying customer: 22~24 cents.