Then that's an opportunity for Adsense...isn't it?
You do have a certain point about the slimming margins in PPC. There are a lot of knuckle heads overbidding for terms. As soon as they realize they are not making money there is another one to take their place.
If you want to make some money I would consider becoming a retailer so you could buy products at wholesale. You then have a whole lot more margin to play with. You can then bid higher for PPC or better yet become a power seller on Ebay. You can't ask for more targetted traffic than Ebay.