The details:
I have a daily emails newsletter which, basically, acts like a blog. I write a story sharing some true, typically unknown item (Abe Lincoln created the Secret Service the day he was shot, for example) with the readers. I'm not putting the URL here because I want to be clear that this question isn't intended as a promotional vehicle.
The email costs me $50/mo to send. (I'm using Mailchimp and that's their monthly fee.) It'll cost me $75 when/if I break the 5,000 subscriber plateau. It's not expensive, but I'd like to break even, and I'm looking for easy ways to get there. (The list is waaaaaaaay too small to consider direct sales brand advertising.)
I can't run AdWords or, for that matter, any standard ad network's banners, because the content is delivered via email. I occasionally drop in an Amazon affiliate link but I don't want to overdo it. (Perhaps a "Book of the Day" line would be good, or "Related Reading.")
I'm looking for ideas which are out of the box. Anyone?
If you always write about surprising stuff, find books that map to that: http://www.amazon.com/Never-Shower-Thunderstorm-Surprising-M...
Sponsors are good too but require a bit more hustle.