1. Depends what you're selling. I believe that the product topic is the prime mover. Unless you have something that people desperately need, your subject just blows out into the vast ether we call information overload. The way you can tell your desperate product solution works is by old fashioned viral marketing... word of mouth/email/Twitter/Facebook/Youtube.
2. A 19.95 book that breaks even with PPC should only act as an entry point for a big upsell. But vast profit can be made without that: fatloss4idiots.com got $21million sales last year solely with a $40 ebook, using the next step...
3. Article marketing. Still works. I've set up my Lotto Affiliate Center http://www.lottoaffiliatecenter.com
) almost entirely round the concept. I've written 800+ articles via daily newsletter to my blog (www.silverlottoblog.com) over the last few years, and it's rare that I don't get 10-20 sales a day from that source. fatloss4idiots.com uses that kind of promotion mainly.
4. My products convert at 4% unique visitors. fatloss4idiots.com converts at 2%. Plenty of opportunity out there still!