And it costs a lot of money. Yes, you can do postings to Usenet groups that are tasteful, but it isn't the same as sending a full direct mail package. There are a few newsletters in the travel arena. The one that comes to mind is the Consumer Reports Travel Letter published by Consumers' Union. I wouldn't necessarily rule out sponsorships.
Sponsorships are damn hard to set up though.
Or you could offer trial subscriptions to ticket buyers, etc. In short, I think it's extremely important to understand marketing and then apply that to the Internet. If you're thinking about a newsletter, then be sure that you know a bunch about newsletter publishing. I don't mean you have had to do it, but do research and read some books and trade magazines about it. Applying that kind of knowledge to the creation of an e-newsletter makes it more likely that you will succeed.