Old house, cast pipe under the crawlspace

Recip saw with Diablo carbide-tipped or a Lenox diamond abrasive blade if you have enough access. I've done the same work under my house, not fun but those blades make quick work of cast iron.

That's what my plumber used. And get the heavy duty ones. They have a pic of a pipe on the side of the blade.

Bout to have a plumber replace the cast iron waste pipe in the crawl space under our kitchen. It’s about 60 years old. No leaks but the interior diameter has been shrinking to the point that it barely drains. I contemplated doing it myself but the pipes are a little more complex than I was expecting. So now it’s a waiting game to see what 15ft of pipe is gonna cost me

Good stuff guys. Thanks a ton