Yes, it will be extremely expensive and it's a crime that we don't tax fossil fuels to account for those negative externalities. I don't want to downplay it too much here. It's serious business, but is not the end of civilization - unless those feedback loops kick in in a big way. I think the change in sea level will be somewhat gradual, giving time to migrate or fortify infrastructure. Keep in mind few of the roads, bridges, and skyscrapers in our current cities will still be there when the water reaches them. If we write them off and build further inland instead of trying to maintain or rebuild them in place, it will naturally shift part of our infrastructure. It will still be costly though.