That template could be written on a single line: I have just spread it out for readability on the forum. It’s a horrible data structure from that URL: basically HTML-in-JSON, and the sensor will break if they change anything about the layout.
The last bit of the template takes the result from the lookup, which is <p>€ 1,15</p>, swaps the decimal comma for a decimal point, and discards anything that’s not part of a number.
Paste the response from the URL into JSON Viewer Online Best and Free and click “JSON Viewer” to find the paths for the other values you want. Here’s the one above so you can see how the path on the tool maps to the JSON lookup in the template:
Thanks @Troon, that really helped me setting up the first rest sensor.
For the other two, I’ll get to them later this afternoon. I don’t expect that it would be an issue with your explanation on the side.