The cost is considerably lower if you watch out for a11y from the get-go, retrofitting it is more expensive since you have to retain the existing behavior, some

The cost is considerably lower if you watch out for a11y from the get-go, retrofitting it is more expensive since you have to retain the existing behavior, sometimes of existing and complex but non-accessible components. Add to that the need to e.g. caption all the existing pictures and it gets even worse.