No, there is no extra fee if you file your US trademark on the "use in commerce" basis (1a).
The "use in commerce" option means that the trademark is currently being used in commerce on the US market. In such cases, the USPTO requires proof of sales, also called a specimen. This can be, for example, a screenshot of your website, product packaging, advertising materials, invoices etc. The specimen must be attached to the application when filing.
Please be careful to attach the correct specimens. In case your specimens do not meet the criteria posed by the USPTO, they can be refused. In such cases, you will be asked to provide a replacement. Otherwise, your trademark cannot get registered.
If you are not selling on the US market when filing your application, you can proceed; however, you will need an "intent-to-use" application. In this case, a follow-up fee is necessary.