This chart shows recent sales on msabundle.com where I sell contract document templates for freelancers and consultants. Nice, eh?
I started the project a little less than 2 years ago and have experienced very slow but steady growth in revenue over that time. For the most part it's a side project that I have ignored on a daily basis, especially so during the first year and a half when I only got a few sales a month. I say that ecommerce takes patience, because there were a handful of occasions during that time where I wondered if it was worth the mental bandwidth to keep it going! The ramp up curve was really that flat. But in retrospect, I think part of the issue has been the lag time it takes to get a naturally high ranking for my most effective search terms. I have not done any proactive SEO work like getting bloggers to create inbound links.
Costs? Granted the reason I can offer this service is because of my career experience and lots of other intangibles, but the cumulative hard time investment in creating the site and content over the last two years has to be less than a week. There's only a small amount (2-digits) of cost associated with hosting the site, so the margin is almost 100% profit. A perfect lifestyle business and the mailing list of customers that I'm building up is invaluable for marketing my other projects such as the monthly Consulting Masterclass and my new book about consulting.
Really proves out the value of selling your byproducts! (Thanks Jason and 37signals for popularizing the concept!)