Are monthly management fees a waste of money?

I might not be addressing the right audience here, assuming many of you are PPC managers, but I'll ask anyway.
Is it reasonable to pay $1000 per month indefinitely for someone to manage my PPC account? My ad budget is modest at $5000 per month. Once we establish effective campaigns, I prefer to handle the budget myself. I question the necessity of allocating 20% of my monthly ad budget to a manager. Am I mistaken? I'd appreciate your insights on this matter.