Apartment Prices

I’m not sure how this would work exactly but I wonder if there might be a way to track updates in apartment prices in the user’s local area.

Do you know of a data source that provides this information, ideally with an unauthenticated JSON API?

Seems like Zillow may provide an API that helps with this in the US.

I was wondering about doing something similar for the UK using Zoopla. My thought was to show an alert for new listings, rather than just prices.