To restrict sales to specific categories, please check this doc: How to restrict selling to specific listing categories - HivePress Help Center. If you have CLASSIFIEDS as a custom attribute, you can also restrict it to specific categories. Please go to Listings > Attributes > edit attribute > and select a category on the right sidebar.
Please provide more details on how you added the price attribute, as there are two options for restricting it, using custom attributes or the price attribute from the Marketplace.