What they actually cost

The usual comparison is one line long: WooCommerce is free, Shopify charges every month. Both halves are true, and neither is the number you'll actually pay.

WooCommerce: free plugin, paid store

WooCommerce is an open-source plugin for WordPress. Installing it costs nothing. Running a store on it does:

• Hosting. You need a server that runs WordPress well. Cheap shared hosting works until your first busy sale day. Managed WordPress hosting costs more and is worth it.
• Extensions. Subscriptions, bookings, advanced shipping and many payment gateways are paid extensions. Most are sold as yearly licences, and you need to keep renewing them to get updates.
• A theme, if the free ones don't fit your brand.
• Payment processing. Your gateway (Stripe, PayPal and so on) takes its cut of each sale, just as on any platform.
• Your time. This is the one people leave out. Someone has to update WordPress, WooCommerce and every plugin, then check that checkout still works afterwards.

Shopify: one bill, then apps

Shopify charges a monthly plan fee, and the hosting, security and checkout come with it. The costs that grow over time are:

• Apps. Most Shopify apps charge monthly. A store that runs five or six of them can pay more for apps than for Shopify itself.
• Payment processing. If you use Shopify Payments (where it's available in your country), you pay card fees. If you use a third-party gateway instead, Shopify adds its own transaction fee on top.
• A theme, same as above.

The difference is the shape, not the size

WooCommerce has low fixed costs and unpredictable variable costs, most of them paid in hours. Shopify has predictable monthly costs that grow as you add apps. Which is cheaper depends almost entirely on what your time is worth and how many features you need.

How to compare them honestly

1. Write down the five features your store can't live without: subscriptions, local delivery, bundles, whatever yours are.
2. For each platform, find what provides each feature (built in, an extension or an app) and its price over 12 months.
3. Add hosting (Woo) or the plan fee (Shopify), plus payment fees at your expected sales volume.
4. For WooCommerce, estimate maintenance hours per month and multiply them by what an hour of your time is worth.

Check prices on each vendor's own pricing page. They change often enough that any figure in a blog post will be out of date.

Free software isn't a free store. The real question is whether you'd rather pay in money or in hours.

Next: who's on call when checkout breaks.