5S on/off button replacement cost

[adam9c1]

I know when I had iPhone4 the on off button was worn out. Still worked each time but I had to press harder than normal.

I have noticed recently with my 5S it is slowly getting there. I feel like the button is not sticking out far.
I plan on not replacing the phone anytime soon.
What is the average cost of replacement button AND labour at a reputable shop?