What is the best way to make many sites with almost the same content for different cities on wordpress?

Question

Search Engine Optimization

There is a wordpress directory with a custom theme. The customer wants to make a few dozen more (and maybe more) copies of the site on different domains, which should differ only in the page with contact information. At the same time, the main catalog must be the same and the product must be added to the catalog once in one place, and not separately for each site.
A multisite, as I understand it, is not quite suitable, because it assumes separate content for each site and, accordingly, it will be necessary to add new pages separately to each site, and the tables and contents of wp-content / uploads will be duplicated for each site, plus the more the site, the more server load.
Are there any adequate solutions for situations like this or is it a bad idea, given that most domains with duplicate content will not show up in search or get banned? And is it better to make one site, to which to add a contact page for each individual city?

Answer 1

10 subdomains leading to one site.
We write a functional that determines the current subdomain.
We have records where the name of the region, its declension, URL address, contact details.
We write a modal for changing cities based on records about regions.
Total: At hand we always have an array about the current region, respectively, knowing the current selected region / subdomain, we substitute the contact details in their places. Everything