Blog writing for accountancy site

I have two sites. One for my accountancy business and one for my payroll business. Both need a weekly blog. I'll be able to indicate a keyword or idea perhaps with links to other online content.

Indicative budget is therefore per week and this could turn into a long term job. With other sites likely to be added.

A good understanding of English is vital as the posts have to be a good read as well as keyword rich. I would suggest around 300-500 per words per blog.