Ceramic coating it would likely be the cheaper route to take. I've never had an issue coating a cast iron exhaust manifold so I don't see why anyone would advise against it. Just make sure it's coated both internally and externally. I'm not sure who still offers coating up there, but my go-to for porting and coating these days is Ruben @ SoCal Porting.
https://socalporting.com/
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