Why not just do a simple cross-link partnerships with other sites (like Century of Flight, Warbird Depot, Military Factory, World War II Database or any of thousands of others) that cater to the same people. No money has to exchange hands and the sites can monopolize on the increased traffic monitarily by whatever means is appropriate to their business model. I know I've never seen links like this on the AH website (other than player postings) but I'd consider it a service if they were interesting to me.
Back in the day when I was in charge of marketing for a commercial website I did this all the time with reasonable success. The ROI was good considering the time it took to to vette the sites and write a contract but most of the contract was boilerplate.
Guerilla marketing would also be a cheap, high ROI model. Send a cheap givaway (a button, patch, CD, etc.) to all the airshows and air museums. People love free stuff. What airshow promoter isn't going to accept a "value add" to give away to ticket buyers? And many of those people's interest will be peaked enough to check out the website as long as they have a reminder in their hands.
Yes, there's a little effort involved but very little cost. I used to hire interns or entry level marketers to execute on these things.
Of course you probably also want to maintain a targeted ad campaign as well as a coordinated publicity (sorely lacking for HTC from what I've seen) campaign to fully capitalize.
I've seen HT say he doesn't have faith in traditional marketers. I think he may have simply had a bad experience with an inexperienced (or substantially overqualified) individual.
