Karin, doing a demo is a great idea. As a portrait artist, looking to learn more about portraiture, I would never buy a still life demo, simply because I relate what I see on the cover to what I expect the content to be about.
Ask yourself what message is it that you want to pass along and who the target audience would be. Portraiture is the hardest thing to learn, but with a teacher who can think like a beginner, pitfalls can be pointed out to help even the freshman along.
I would suggest renting a couple of videos and judging what you like or dislike about the varied teaching methods.
Also, you might contact Alexei Antonov and ask him about his success rate on his DVD's and down loadable instructional offers. I did buy his DVD on how to paint grapes, but that's because I really wanted to learn how to do that.
