I’m actually going to post an article about the evolution of the comic book format, but basically, ads provide a lot less revenue that you’d think because circulation numbers are so low. Marvel, DC, Dark Horse and Image can get away with selling ads because they sell enough books that they can claim high circulation. But these ads aren’t really targeted and are essentially worthless since they generate so many repeat impressions; advertisers aren’t paying a lot for them.

Your idea is interesting, since you’re basically saying “why not make a small amount of revenue while helping to promote other small publishers?” I would suggest, however, that these publishers would have more power banding together under a single brand than they would cross-promoting one another’s books. Also, generally cross-promotion occurs with a trade — “you promote my book, and I’ll promote yours.” So charging money would just complicate the process.

An alternative would be to offer to publish pin-ups of characters with fans (at their request) and charge $25 per page. Keep in mind, though, that you could only use your own characters to do this, since anything else would be copyright infringement.

Advertising is a tough topic, because so many people talk about it as if it’s a guaranteed source of revenue. But really, it requires a proven product and a dedicated sales contact, so it’s as much work as anything else.