Informative SEO articles

I am looking for a long term relationship with a skilled article writer. I normally need between 5 and 10 articles each month, and each articles has to be about a certain topic and contain curtain key phrases. Requirements: * SEO friendly!! Key phrases and wanted density will be provided. * Informative and correct, the writes MUST do solid research about the topic. * Original content that have to pass Copyscape. * The articles must be written with perfect English grammar and spelling. (US English) * I need all rights, but the writer may be credited with name if he or she wants to. * Minimum length for each article is 600 words Please tell me how much you charge for each article.