Beyond Educational Content It sounds like the potential business model and instructional approach are based on a publishing or broadcast model -- creating content that people might be interested in paying for, then selling it to them and letting them watch/read/listen to it. In the pre-Internet world, that model seemed to work pretty well for many companies, but I believe that it has limited potential now. It will become more and more difficult to sell information that isn't exclusive.
Blame Google if you want, but people expect information to be free. There is enough info out there on nearly any topic you might care to explore in greater detail. Most people won't even register at a site to get something -- even when it's free registration -- because we all know that we can find the same info elsewhere without the hassle. Instead of creating more information/content, focus on helping people use the information (mostly free) that's already available.
It's a bit like the old fishing parable: give a man a fish and he'll eat for a day; teach a man to fish and he'll be fed for a lifetime. On the net, the fish (info) is all free or will be soon. It is not possible to collect and give everyone all the information about every slice of military history they're interested in, but perhaps you can teach them the process of figuring it out for themselves, guiding them through the tough spots, and connecting them to other people who share their interest.
Aside from the business model implications, some of this is pure Bloom's taxonomy. Educational publishing generally assumes a passive audience who will be subjected to the information provided. Maybe there are chapter questions or suggested activities, or links for further research, but the publisher doesn't really care much about the learning. Watching, listening and reading all tend to be at the shallow end of the taxonomy, right? The deeper stuff is all about creating context, discussing implications, combining disparate ideas, teaching the content to someone else, applying, creating, using new knowledge, collaborating, and solving authentic problems.
From a marketing perspective, I'm thinking that your target market may be interested in learning about their slice militaria (mostly history), but only as far as that information meets their more important desires. Their real needs are personal and goal-driven: "I don't want to get ripped off when I'm buying or selling artifacts" or "I need to know how to find experts in the specific area I'm interested in", or maybe "I want to be able to figure out which artifacts will increase in value over time". Those are the leverage points -- solve those problems for them and they may be more likely to pay.
Instead of telling viewers about the history of an army unit, connect clients to a message board on the topic that already exists, along with ideas about how to glean information from that online community, maybe even drawing attention to the community leaders and offering advice for starting out. Connect them to books from online booksellers (and collect the commissions) that you as the knowledge expert have found useful. Link them directly to online militaria sellers, along with specific advice identifying things to look for, reputation, potential pitfalls, and valuable background information -- negotiate a commission with the sellers if your referrals lead to sales. Teach them to live and breathe eBay. Focus on the process of helping customers find the best information and applying it to their goals. This is more of a consulting role, rather than an information-provision role.
Designers sometimes talk about using the magic wand method of figuring out what they should be creating. If you could magically create the perfect product for your target market, what would it do? I don't know enough about yours to really say, but it might be like a robot of some kind, sitting beside your customer and providing them with the perfect knowledge and advice to make the most money on every sale and find the best bargains for every purchase. The robot might know everything about the client's interests, inclinations and weaknesses, figuring those into every calculation and suggestion. Maybe it knows everything about every piece of militaria ever sold, including projections of future value. It's a fanciful exercise, but helps focus discussion on what people really want -- then you can try to determine which components of the magical product/service could actually be created, utilized or attempted.
My guess is that if you consider any of these ideas, they may lead you in the direction of becoming an expert in the field and selling that expertise instead of the background information. You could become a sort of broker or consulting specialist for the trade. Instead of selling a couple of hundred informational DVDs in a year and covering your costs, take a 5% commission on the sale of a dozen $2,500 artifacts, and buy and sell the stuff yourself for profit if it's what you enjoy anyway. Join and create communities to make the connections that are lucrative and interesting for you.