It depends on the editor of course, and the type of work. Developmental editing (or Content Editing, i.e. Plot holes, plot structure, character development, consistency, accuracy) is the most expensive and can be around $50 an hour. It is also very difficult to quantify how many hours people will need to spend on it - if the novel is very sharp already, 5 to 10 hours.

Copyediting (sentence structure, style, etc) would be around 45$ per hour. Consider more or less 2000 words per hour.

There are cheaper editors around. I am a believer that you have to pay the right amount of money for the right work. Also, every editor is different, and more expensive doesn't necessarily mean better for you.

For a content editing, you're looking at someone with a sensibility similar to yours and maybe versed in your genre (though some people prefer editors far from their genre). For Copyediting, you want someone who will understand your style and polish it; I've seen many editors changing and clipping and moving. A good editor does not tame your style, but understands it, and simply makes it shine.

Then you have line editing and beta-reading.

I know many people on this sub would skip the professional editing. I say, try anyway. You can always bargain. Wash cars. Dishes. Walk dogs. I mean, find an exchange their service if you cannot afford one. First, you will have a much more professional work - which would have more chances to impress an agent / shine in the pile of unedited average of self-pub. And secondly, and more importantly: you LEARN a lot from an editor. They've seen so many manuscripts. They will be true to you, and tell you the truth, because that's why you're paying them. You will have the comments and the highlights and the suggestions, and this will help you detach your eyes from the novel / your style, thus making you analyse yourself.

tl;dr Good editors are expensive because their work is quality. You can always find a bargain for your needs. Editor don't just make books better, they make writers better.