Usually at AdCentre, now Bingads you can get lower PPC rates, especially for your niche. To get your PPC right and weed out non-converting keywords, some clicks would have to be spent. So tweak your keywords and identify nuggets at lower cost using adcentre. Then run ads on both adwords and adcentre to see which convert better.
They are two different services man. Adsense is right for you but AdCenter (as known as BingAds) is the place where you spend money to get the traffic - NOT making money from your traffic.
Yahoo Network provides the ads to other websites but the requirement is very problem where they require more than 10K unique visitors per day and the traffic have to be good also.