My tailor charges $15 per shirt to slim the body and sleeves. He opens up the seams that run down the sides of the shirt and underneath the arms, removes fabric, and stiches them back together.
I have another tailor that I use for more delicate things, such as suits, and he charges $24 per shirt. He is located in an expensive part of town with expensive real estate, and he has a fantastic reputation, so that would explain the price premium.
Most of the area I live in would meet that definition. Sleeves cost 10 to shorten (from the shoulder) ten to taper sleeves, fifteen to taper the shirt on the side seams like yours does. just the taper would be 20 normally, 18 for me, or 15 because I'm having a bunch of other shit done to it. She'll occasionally toss me a freebie like replacing all the leather buttons on a tweed SC if I ask (I let her keep the old ones) or free collar extenders, etc. Last time I had her taper some chinos, she didn't charge me for the hem either.