"Tune Smith" wrote:
In Europe, they have 500-year old buildings. How long do water pipes
last there, and any methods for making water pipes last longer than 30
years?

Doubt too many of the 500 year-old-buildings came with indoor plumbing as
original equipment. For th first few hundred of those years "running water"
probably meant running out to the backyard or neighborhood well. And the
oldest plumbing was usually lead pipes...that's got its own set of problems...

What are the options (preferably less expensive) for "plumbing
problems" like leaks in a 30-year old building?

Depends on the cause. If the water is real corrosive, fixing the current leaks
and putting in some sort of whole-building treatment dingus might be cheaper
than the $90K quoted. Depends on how thin the pipes have gotten.

Should a second (or even third?) opinion be obtained before spending
$90,000 on pipe replacements?

For that kind of money, I'd want lots and lots of opinions.