Custom WordPress plugin developer

Plugin cost is driven by how much of WordPress the plugin has to touch. A plugin that adds one admin screen and one shortcode is a small build; one that registers custom post types, adds Gutenberg blocks, exposes REST endpoints, and synchronises with an external CRM is substantially larger. Both are quoted after a scope call that specifies the behaviour in writing.

Because functionality in a theme disappears when the theme is changed or updated. Anything that is behaviour rather than appearance belongs in a plugin, which is why customisations added to a theme's functions file are one of the most common causes of a site losing features after an update.

Plugins built on WordPress's documented hook and filter APIs survive core updates, because those APIs are what core commits to keeping stable. Plugins break on updates when they bypass those APIs to query the database directly or override core behaviour, which is precisely what building to coding standards avoids.

Yes. Work on an existing plugin starts with a review of its structure and a written assessment of whether it is safer to extend it, fork it, or replace it. Where the plugin belongs to a third party, extension through its own hooks is preferred over modifying its files, since direct edits are erased by the next update.

Yes. WooCommerce is itself a plugin with an extensive hook system, so custom shipping methods, payment gateway integrations, checkout field logic, and product-type extensions are all built the same way — through documented WooCommerce hooks rather than by modifying WooCommerce itself.