No idea who might know this, I don't have a clue. If you gathered 1000 or 5000 emails in a niche market. How much could you charge someone to send out emails to those people. Of course they would have to opt in to the emails.
It depends on how you get the list. If you get them from subscribinh to your site it wil be a good list. But if you get it from other people, it will make no sense.
I haven't started yet. I got time to do 1 of 2 jobs. These would be emails from a specific source of people. Good emails definately. Not that bulk junk email lists that are being sold. I like darren's idea