It really depends on what you're offering. If you just make a PowerPoint equivalent to the Web Hackers Handbook, why would it be worth more than the $50 or so dollars for that resource? If you provide audio lectures, instructional videos, challenges/labs, etc., it could be worth significantly more. The others also have the benefit of being relatively established with a potential certification that can be listed as a credential as a resume. The possibility of opening doors provides additional value.
Something that might be interesting would be to take a piece-meal approach to the course and offer various modules (XSS, CSRF, SQLi, Advanced Oracle, Web Shells, Java, Flash, etc.) as $50-100 units. You could possibly offer bundle/subscription pricing (for new modules) as well. This would be useful for some people who may want to brush up on a couple topics, and would be disinclined from purchasing an entire course to do so. At the same time, discounts could be available for someone that wants everything (to briefly answer your original question; I'd say anything from $300-1500 is feasible, depending on what is offered.)
Regarding content, what I really want is to know everything about everything
Seriously though, you need to balance breadth and depth (that's what she said?). I don't want to be given a high-level overview of a bunch of topics that leaves me with little-to-no practical knowledge, nor do I want to focus on a small number of techniques in excruciating detail that would limit my effectiveness in the real world (i.e. I can only compromise an app in specific scenarios/configurations, even though many other avenues may be available). If you could find content that satisfies the 80/20 Rule/Pareto Principle (80% of the compromises are achieved through 20% of these known vectors/techniques), you'd be off to a good start.
Furthermore, I want to apply what I learn ASAP. You don't need a full-featured application for every point, but something like a collection of PHP scripts would be useful. For example, when discussing XSS, the first script could just take echo the 'q' GET variable back to the user, the second would apply basic filtering and require some encoding, and so on. I really appreciate exercises that reinforce what I'm learning and show me how they can actually be applied/executed.
That was a bit of a ramble, but I HTH.
The day you stop learning is the day you start becoming obsolete.