If you want the unique article at cheap rate then you should write the articles by yourself. And if you hire someone to write the article then it may be some costly. Because for the quality content the writer must give some to write the article and for that they may charge more than your expectation.
I would agree that the cheapest way to get original content is to write the content yourself. What article you want isn't as important to finding low cost articles. The real problem is finding writers who are cheap, but still provide high quality, well written content. Most American writers require more money because the cost of living in America is higher. The best option right now is to find writers from South Africa. The cost of living is significantly cheaper there, and you can find native English speaking people with college degrees who will write for you at extremely affordable rates. Regardless of where you find a writer, the biggest problem is going to be in finding a quality writer who can create quality content that is valuable to your readers.