there are 5 levels of editing.
see detailed description elsewhere in forum discussions.
see here to find several of them: http://www.writersdigest.com/forums/topic/what-are-the-five-levels-of-editing
this site has a good 5 level summary
the short version is (per william adams at first link above )
Developmental Editing – Concept Level Editing
Substantive Editing – Paragraph Level Editing
Copy Editing – Sentence Level Editing
Fact/Accuracy Checking – Information Level Editing
Proofreading – Word Level Editing
note some folks combine tasks above and only use 3 levels of editing and some use more detail to have 9 levels.
as to price: you get what you buy. make sure the editor you hire is in tune with you and how you write.
development editing may cost more than the lower levels of editing depending on how much help you need to organise your book logically.
the publisher might provide the final low level of edits but you need a logical well organised book to get a publisher. You usually need that to even get an agent although some agents might work with you if you do not need a lot of help structuring the book.
before hiring an editor i would research your approach and try to get it as organised as you can before paying for help. if you are writing fiction then try to get as far along as possible, BEFORE ACTUALLY WRITING ANYTHING, to have a framework for an editor to help you with. Without that you are essentially asking the editor to do your plot for you.