Minimum profit is not the target you should be aiming at. I would suggest shooting for maximum profit. :)
You may be interested in knowing what your maximum CPC should be then determine if you can be competitive in your Adwords market with that maximum CPC.
You can determine your maximum CPC by knowing some data from your existing website and then running some tests.
If your book sells for $10, how much of that is profit, after you get rid of all of your fixed costs.
Then determine how many visitors to your website until you sell a book (your conversion rate). This will tell you how much profit you can generate per visitor. Once you know this number, you will not want to bid above this for a click.
Example: You make $5 off the sale of each book and every 20 customers to your website results in a conversion (sale of a book)  $5.00/20 = $0.25. You want to make $.25 your maximum CPC in your adwords campaigns.
You can adjust these numbers accordingly. And make sure to optimize your ads and your website to increase your conversion rate.