Yes, you do need an editor. It does not matter how many times you read and re-read your own work, you will be blind to your own mistakes and inconsistencies. Friends and relatives may not be objective enough and spellcheckers at times cannot recognize errors such as using a word that is correct in itself in the wrong context.
Shop around for the best rate, usually given by word.
I am a copyeditor, so I know what I am talking about.
Good luck!
Thanks for the input! Does her rate of $3.00-5.00 per page seem reasonable to you?