Not sure what type of editor you're talking about, but a copy-editor sorts out all your weird punctuation and lack of cohesion and they don't tend to cost much. It's the ones that help with story structure (don't know what they are called) that are prohibitively expensive for DIY writers.
I used to think I don't need one, being able to copy-edit other people's work myself, until someone gave me a free trial. I got a bit of a shock
If you can't afford anything at all, there's always this but don't expect magic from a computer program.
http://prowritingaid.com/Free-Editing-Software.aspx