You need to find a company that will give you a primary yahoo feed - parkingplace, redirect.com, ddc.com, parklogic, dotzup, trafficz, etc. Some allow bought traffic some don't but you'll need to apply for it and they usually expect a large portfolio and will have strict guidelines to follow.
The problem is you need traffic that actually converts for the advertisers and most of the inexpensive traffic won't. You get what you pay for and that sort of traffic is often fraud, fishy, or just poor quality. The days of sending cheapo traffic to your mesothelioma/structured settlement sites and banking hard are long gone.