Agree with @SpreadsheetMom that the free resources at College Essay Guy are useful (our HS recommends them too), and did you know there are also members here at CC who can help give feedback on essays? Follow These Steps to Get FREE Essay Feedback
From people I know at my HS who paid for essay coaching for their students, a lot of the value is just helping to structure the process and having a non-parent available to nag the student to write drafts. What you don’t want, though, is an essay coach who tries to turn the essay into what they think colleges want, and interferes with your student’s genuine voice. Sometimes a paid coach gives too much help that way.