"Like this guy he came to fix a leak and saw other pipe adjacent to it ... and he evaluated that to be out of code without my asking ....."
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In and of itself, that is not bad. A good tradesman, like a good professional in anything else, SHOULD be on the look out for other problems and bring them to your attention. So your "without my asking" is not a reasonable stance to take on your part.
The fact that you have NOT been told precisely what the violation is, however, and have not been given an extimate range (you said the lady was vague), AND the fact that grandfathered situations are legal, however, tell me that this plumber is trying to generate work. Tell him you want detailed facts about the code violations and his estimate range (cut some slack on this -- there could be stuff in the wall that will cost more and he won't know about it until he opens it up). Then get some other evaluations and estimates.
If the conditions merit remediation, use a plumber you trust to make the repairs. If it's a grandfathered condition, consider letting it go UNLESS (and this is my opinion) it is lead pipe. Lead pipe you should replace, regardless of legality. Do you really want to risk poisoning kids in order to save a few bucks?