Copy Writing - Document Improvement

I am looking for somebody to sharpen up the language on documents - proof them, tighten the language and where possible, make it more snappy.

I have around 15 to 20 articles I am writing, each one is between 1000 and 4000 words, with most around 3000 words.

I would like to know the costs per 3000 artcile for the following:

Proof
Language Improved
Consider tightening the language where possible - to be made more snappy

The content for each article relates to technology and financial services, but is designed to be read by those without a deep understanding.

The articles link together - i.e the different articles reference each other, so build up a wider story.

I would like to know the intial pricing for this and the timelines for the first article.

This is all in English and the first language should be english.