I'm not 100% sure, but I came across questions that asked contributions to google maps (local guides) that asked the $ rating of a restaurant. So part of it might be local guides wandering question about the place when google needs the answers.

If you want to show that they are and expensive or cheap place you can suggest an edit to add their menu which has there prices.

And if that isn't what you're looking for, you can write a review detailing the price range.