The most cost-effective approach is usually:

1) Use one headless CMS as the single content source

Pick a CMS that supports:

• multiple sites / tenants
• content reuse
• localization or variations
• API delivery

This avoids duplicating editing work across sites.

Good cost-effective options:

• Strapi or Directus if you want self-hosted/open-source control
• Contentful / Sanity if you want managed SaaS and faster setup
• Ghost or WordPress headless if your needs are simpler and you already use them

2) Model content for reuse, not per-site duplication

Design your content types so one piece of content can power many sites:

• shared articles
• shared product data
• shared author profiles
• site-specific metadata, branding, or overrides

Use:

• global content blocks
• references/relations
• site configuration entries
• local overrides only where needed

This cuts editorial and maintenance cost the most.

3) Use one frontend codebase with multi-site configuration

Instead of building a separate frontend for each site:

• use one app or monorepo
• map each domain/subdomain to a site config
• load site-specific theme, navigation, and content filters at runtime

This reduces development and deployment overhead.

4) Publish through an API, then cache aggressively

To keep hosting costs low:

• fetch content via API at build time or on demand
• use CDN caching
• use static generation or incremental regeneration if possible

A common low-cost setup is:

• Next.js / Nuxt / Astro frontend
• headless CMS
• CDN + static or hybrid rendering

5) Separate shared content from site-specific presentation

Keep:

• content in the CMS
• design and layout in the frontend

That lets multiple sites reuse the same content while each has its own brand look.

6) Automate publishing workflows

Use:

• scheduled publishing
• webhook-based deployments
• preview environments

This reduces manual work and mistakes.

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Cheapest practical architecture

If your goal is lowest total cost:

• CMS: Strapi or Directus self-hosted
• Frontend: one Next.js app for all sites
• Hosting: one small cloud instance + CDN
• Delivery: static pages or ISR
• Content strategy: shared content with site-specific fields

This is usually the best balance of:

• low license cost
• low duplication
• manageable maintenance

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When SaaS CMS is cheaper

A managed CMS can be more cost-effective if:

• you have a small team
• you need to launch fast
• you don’t want to manage infrastructure
• editorial users need reliability and support

You may pay more monthly, but save time and ops costs.

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Rule of thumb

• Few sites, limited team, need speed: managed headless CMS
• Many sites, strong dev team, cost-sensitive: self-hosted headless CMS + shared frontend
• Very simple publishing: consider whether a traditional CMS with multisite support is enough

If you want, I can suggest the best stack based on your number of sites, team size, and budget.