I offer both copyediting and proofreading services, depending on what your project needs. This article from NY Book Editors an excellent delineation of the difference between copyediting and proofreading. This article from Wendy Laura Belcher is a good guide to how to work with a copyeditor.
My current rate for copyediting is $35 per hour. Copyediting entails a close and attentive reading of both micro and macro aspects—grammar, spelling, punctuation, other mechanical elements, and overall structure, flow, clarity, and cohesiveness.
My rate for proofreading is $25 per hour. Proofreading is the final pass after a text has been copyedited.