Proofreading/Copyediting Pay Scales

Long story, short: Friend of mine wrote a 75K book on a subject we're both well-up on.
Was asked to proof it. Did so (rush job!), and in addition to addressing the basis tasks at hand, noted more than a dozen segments structured in a manner I thought he'd be well-advised to rethink -- and 80% of those suggestions were accepted, in toto.

Was offered $2 a page for the work, and took it. What's the general market compensation in this area? Thanks.