All the data is stored on your phone, offline, and it's not available anywhere else. So only you are the owner and responsible for your data as it should be.
CostList uses Google AdMob to show ads in the app. Google Admob can get information about how many users are seeing and interacting with the ads. Third-party vendors, including Google, can show ads in the app based on the profile Google has of you. You can check your ads settings here. This information is anonymous, and CostList can't do anything with this information. Google AdMob is in control of this information and you can see its privacy policy here.
CostList uses Google Play Billing for let the users pay for an in-app purchase to remove the ads from the app. The purchases of the app are completely anonymous and CostList can't access any of the payment methods. All this information is in control of Google Play and you can see its privacy policy here.
CostList doesn't use any third-party analytics. As a result, CostList doesn't log any information about you or your behavior using the app and has no interest in doing it.
CostList does not collect, transmit, distribute or sell your data.