Best way to hire freelance journalists to write blog posts cost effectively?

Where is the best place to get freelance journalists to write high quality blog posts on my niche (mobile apps)? Some of the sites I looked at are either too expensive per post or it doesn't seem like the quality will be there.

Expensive & high quality are somewhat vague - you can check for marketing article providers on "warrior forum" type boards ( http://www.warriorforum.com/tags/article%20writing.html ) for $4 / 1000 words deals, or hire professional journalists at professional rates based on content type ( rate source http://www.londonfreelance.org/rates/w1000onl.html )

For some, the $4 article will be just as good as the $40 article - but only you as the content curator will be able to make that call.