Depending on the subject matter and if it's purely just writing (many bloggers are required to also post and find photos). 5.00 per post on the low end up to 15 dollars a post for more technical or detailed material.
A writer will be more likely to work with you if you promise a certain amount of work per week or month and you pay regularly.
Post your request with this website:
http://www.freelancewritinggigs.com/
It's a nice community of freelancers and though there's always a deadbeat in the crowd, in general, the response you get here will be a good one.