The rate will depend on your keyword, article quality and requirement. If you just want a normal article then it should charge $2-$10. If you want a high quality article with related unique images, info graphics or video then it should be high from $20 - $100.
I told you previous that rate will depend on niche.
If your niche is blogging and seo related then rate will be low.
If your niche is insurance, auto, real estate, voip and technology related then rate will be higher.