The least complex and most cost effective approach to implementing web accessibility, is to include accessibility in your project requirements at inception. If that wasn't done and your project is already live, you may still be able to act cost effectively if you happen to be ready for a general redesign. This time, as you brainstorm a new design, be sure to request web accessibility compliance that is appropriate for your particular mission before the redesign starts. You'll save money, simplify any required retraining, and likely shorten delivery time.
If, however, your project is already live and you are not ready for a general redesign, your shortest path meaningful web accessibility will likely cover two areas:
- Tweaks to close existing gaps (like adding "alt text" to images that are capable of accepting alt content)
- Widgets that enable users to make certain visual changes to your website in their own browsers, so they can more easily digest your content and use your features (these changes will not actually affect the site itself, of course)
The specifics for each of the above will differ from site to site, so start with an audit by a qualified web professional.