The machinist is being kind to you . A good engine rebuild on the M100 engine will cost a cool $40,000 . If the injewction pump is worn out ,as it will be,there is $2000 straight up (Pacific Fuel injection,South San francisco) to rebuild it.
Pistons are $1000-$1500 each . (I have four new ones if you need them) .

head gaskets are $300-$600 each,
'
If the heads are corroded out and need replacing you are looking at $5000 each.

The Worlds most famous 600 restorer,Karl Middlehauve, said that the 600 is a $200,000 car. By one for $20,000 and it will cost you $180,000 to get it road worthy.
http://www.mbgrand600.com/

This isn't the forum to ask questions about 600's, Go here
www.m-100.cc
There is more than enough knowledge on that site to get the car on the road.
You must realize that there only 2500 600's built from 1964 to 1982 and each and everyone was built to order so parts are expensive .Very Expensive because new parts are just that,New parts made to order ,not stuff that has been sitting on the shelf for 30 years.
And I haven't got into the the real complicated matter of the hydrualics.