My newsletter, Tedium (http://tedium.co), has slightly more than 3,000 subscribers, and produces a lot of content each week—between 3,000 and 4,000 words over two pieces. My strategy for building it out has essentially meant being willing to syndicate these articles far and wide. I currently work with three different outlets (Atlas Obscura, Motherboard, and Neatorama) to republish the work, all of which bring in new subscribers frequently. Eventually, Digg started picking up its articles as well. Basically, it gives me creative license to write whatever I want in my narrow niche while ensuring the newsletter goes out far and wide. I try to reuse every piece so nothing goes to waste.

While it's not bringing in tens of thousands of bucks, it's brought in enough to make it worthwhile (in part through affiliate links—my strategy is to link to the weirdest things on Amazon I can find, with the assumption people will eventually go back to buy something else).

I've also tried to find ways to minimize costs on my end, including switching email providers so that the financial impact of sending thousands of emails every month is small.