Cutting cast iron soil pipe

Question

I need to replace part of my cast iron 4 inch soil pipe with PVC.

What is the cheapest and safest way to cut the pipe to allow me to couple into to it ?

I do not want to smash it with a lump hammer incase I damage the pipe below ground, I would also like a neat finish to the edge of the cast iron pipe.

Kind,

Regards,

Phil Harrison.