A Chrome extension is a small piece of software that runs inside a browser you do not control, on pages you did not build. That is what makes estimating it different from estimating a website.
Price bands
| Scope | Typical cost |
|---|---|
| Single-purpose tool, own UI only | $1,500–$4,000 |
| Interacts with one specific site | $4,000–$12,000 |
| Multi-site, accounts, sync | $12,000–$35,000 |
| Enterprise deployment, SSO, admin policy | $35,000+ |
What drives the number
Whether it touches other people's pages
An extension with its own popup is self-contained. One that reads or modifies another site's DOM depends on that site's markup — and that markup changes without warning. That is not a one-off cost, it is a maintenance commitment.
Permissions
Every additional permission raises review scrutiny and the justification burden. Broad host permissions — access to all sites — attract the most attention and the longest reviews.
Backend requirements
Accounts, sync across devices, licensing, server-side processing. Each turns the project from an extension into an extension plus a service, with hosting and maintenance behind it.
Cross-browser
Chrome and Edge share an engine, so supporting both is cheap. Firefox and Safari differ enough to add meaningful work. Decide before the build, not after.
Manifest V3
Chrome's current extension platform replaced persistent background pages with service workers that can be terminated at any time, and restricted remotely hosted code.
Practically: state does not survive between events unless you persist it, and anything expecting a long-running background process needs rearchitecting. Porting an older extension is often closer to a rewrite than an update.
Publishing
- Developer registration — a one-off fee, currently around $5.
- Review — usually days, longer with broad permissions.
- Privacy disclosure — mandatory. You declare what data you collect and why.
- A privacy policy — required if you handle user data.
Rejections commonly cite permissions that are broader than the described functionality, or a disclosure that does not match observable behaviour.
The part people forget
Extensions break for reasons outside your control:
- Chrome updates deprecate APIs.
- Target sites redesign and your selectors stop matching.
- Platform policy changes require new disclosures.
Budget maintenance from the start — commonly 15% to 25% of build cost annually for anything that interacts with third-party sites. An unmaintained extension quietly stops working, and the reviews reflect it.
Where cost is saved honestly
- Narrow the permissions. Request specific hosts rather than all sites.
- Ship one feature well. Extensions succeed by doing one thing reliably.
- Avoid a backend until you need one. Local storage covers more than founders expect.
- Chrome and Edge first. Add other browsers when there is demand.
If the work is really a web application, a website may serve you better: what a business website costs.