Hello Kcurrents,
Please note that the option to add Best Offer to a Fixed Price listing is dependent on the category. Where eBay makes this available, you should see the option to do so on the listing creation page in a checkbox that is available in the Price area of the listing creation page. If it is available in your selected category, there is a checkbox: "Accept offers from buyers" and if you check the box this expands the price area for the details you can add regarding the Best Offer options.
If you encounter any difficulty using this, please feel free to file a support case from under the Help tab of the site and our support team will be happy to assist you further.
- Craig