Your question is tagged iOS, but if you’re open to using a computer with iTunes, the simplest way is to find the app in the iTunes App Store.
Right-click it, then
Copy Link. Paste the link into a browser, and you will be taken to an iTunes Preview page listing the price of the app.
You can also copy the link using the
Share button on the app’s page in the App Store. However pasting that link into Mobile Safari will prompt you to open the App Store.
Cancel won’t produce the iTunes Preview page, so you'll need to paste that link into another browser (possibly macOS Safari, through Continuity).
Note: Links from the iOS App Store’s
Copy Link command are prefixed with the name of the app. You’ll need to edit it out after pasting it into a browser.
Lastly you could simply use an online search engine to find your app in the App Store:
"Cup the Rope 2" site:itunes.apple.com
The quotes should help bubble your exact app to the top, then you can view the iTunes Preview shown previously.