Even more important than ensuring your content is free of grammatical and spelling errors is feeling confident that your material is clear, concise and correct. Having your content comprehensively copy-edited will give you this peace of mind.
Costs
Every copyedit is different, and the cost depends on exactly how much work is involved. However, to give you a guide, I adhere to the Chartered Institute of Editing and Proofreading minimum price guidelines. https://www.ciep.uk/resources/suggested-minimum-rates/
Payment
A deposit of 50% is required in advance to secure your slot. The remainder should be paid on receipt of the invoice. I accept payment via wire transfer or Paypal. Payment can be made in either GBP, USD or EUR.