A Beginner's Question About AdWords

I have experience as an AdSense publisher-- made a little money with it. I also wrote an ebook and have had success promoting it with AdWords. So, for my next adventure in Internet marketing, I thought I'd try to market other stuff (besides my own ebook) using AdWords. And I'm totally confused. Here's what I did... I found some products that (I thought) had a decent return. Each had a niche market that I was somewhat familiar with. For one particular product, I did a google search and found that there were almost NO ads for products. I figured this would be a decent niche to break into-- no competition. I go to AdWords, set up an ad campaign... design the ad.... make up a few dozen key words... enter my spending limits... click start campaign... THEN I get the messages "[all] 37 keywords are inactive." It wants me to increase my bid to $5.00 per click or $10.00 per click or more. I'm not going to do that. How do I find out what markets will have affordable clicks BEFORE I go through all the work of setting up campaigns? I'm only selling ebooks... I'm only going to make a couple of bucks per sale... I can't afford $10 keywords. I tried to increase "quality" by being more specific and creating keywords that are three, four, five words long. Still, no luck. Expensive. Expensive. Expensive. Why is it that the keywords for MY eBook are only 20 cents... but the keywords for all the other books I want to promote are so expensive? And, how can I tell before I set up the campaign? Thanks for any and all advice.