What is expectation for plumber doing finishing work in bathroom?
I thought this was a bit short but.
It should have been spelled out in the contract. A good price usually means the homeowner doing some of the easy stuff. So if it is not covered in the contract the good price was you doing some of the work. 
As I have been a licensed and bonded contractor I may lean a bit to there side. But there are some real crooks out there and they need to be put out of business. 
This sounds like a mis understanding, and I am sure he will do all the work for a few $ more.