To replace or not t o replace iron pipe to uPVC

Have a dilemma re bathroom refit

I have had two companies assess and give quote. One says need to remove and replace cast iron soil pipe that currently leads to back of toilet. Toilet currently raised apparently to accommodate higher entry lecel of iron pipe. The work would involve getting access via boxed in pipe that runs down through kitchen extension...which would have originally been on outside of house.

Another says he can work with the iron pipe and shave it back closer to the wall and connect new toilet still.

Now the first co. are asking for 1k just for the soil pipe removal and replacement. WHo do I go with!?

I have done alot of reading but can't find anything too definitive. I read of connecters that exist but other sites say they do not offer a guarantee not to leak as they are of different material.

HELP!!!!