Looks like Facebook quietly changed their rules for your Page’s cover photo. It used to be that you couldn’t include contact information, calls to action, or price/purchase information. This limited the use of the cover photo for non-profits and other organizations. Looks like that’s a thing of the past. The currrent rules allow for more flexibility:
Use a unique image that represents your Page. This might be a photo of a popular menu item, album artwork or a picture of people using your product. Be creative and experiment with images your audience responds well to.
All cover photos are public, which means anyone visiting your Page will be able to see the cover photo. Cover photos can’t be deceptive, misleading, infringe on anyone else’s copyright or be in violation of the Pages Terms. You may not encourage people to upload your cover photo to their personal timelines.
To get the fastest load times for your Page, upload an sRGB JPG file that’s 851 pixels wide, 315 pixels tall and less than 100 kilobytes. For images with your logo or text content, you may get a higher quality result by using a PNG file.
That opens up a lot of opportunities to use the cover photo in a more direct manner, without having to pay for promoted posts.