3 Girls' Dad,
I try to put deals like this in a "time" perspective. If he supplied the sand, compressor and the guy to do the work, how much would that cost per hour.
A ball park figure would be $100.00 an hour I think.
If all the parts were blasted 'bright', would this take almost a full work day!
I have sandblasted before, and it is time consuming. I don't think you have been taken to the cleaners.
My bet is that he doesn't do this exact type of blasting often, and his initial bid sounded great to you, but he soon saw the error of his ways.
Most people in this world are fair and decent. If you are happy with the work, then thank him.
Stuart