Copy editing: grammar, word usage, sentence structure, organization, clarity, comprehension, spelling, punctuation. Proofreading: comparative reading of two documents for typos, spelling, punctuation, consistency, and print or electronic specifications. Also, proofreading on hard copy (white-ruler line-by-line reads); this is the most comprehensive proofreading technique.
Rates vary according to nature of copy (nonfiction, fiction, technical, medical) and time frame of project. Reasonable hourly or per-page rates are available.