When processing the RESTcall-response compare the price with the product’s price stored in your database from the previous calls. If they are the same, forget it, if different, do your thing.
There are many different ways to achieve what you are asking for. One option would be to create an entity to store the historical data and associate that entity with a one-to-many relationship to the actual data.
Using a microflow you can match the incoming data to your existing data and create/update as needed under the conditions you design yourself in that microflow.
Hope this helps.