" our property has galvanized water supply lines, it is a 2 story double
with a basement. there is one bathroom with a shower, toilet, and
sink on the second floor, and there is one kitchen with one sink on
the first floor--of course. No bath on the first floor.

For those experienced with the task of supply line replacement, what
cost should I expect if I call in an expert to do the job?

In a way, this seems like an easy job to me, I have replaced many
water fixtures, on/off supply line valves, and added water fixtures to
my current home for outside use. Should I attempt to replace these
supply pipes myself?

Estimates are free. To save money, I used cheap local labor to do all the
ditching, then got plumbers' estimates for the copper piping job, awarded a
contract, then left the ditch and pipe exposed for a week to make sure all
joints were leakproof, before burying the line.