Some years ago I used mobile phone or internet rates (for example, with basic fees and a given charge per minute or by data volume) to introduce and motivate the study of linear functions.
However, today (at least in Germany) most people have flat rates (or some semi- flat rates where the data speed is throttled after a given GB volume is reached). So mobile phone and internet rates are not ideal examples for students anymore.
Question: Are there other examples that students (in my case, they are ~15 years old, most of them boys who are also interested in technology and science) may find motivating and that also have the didactic clarity and variability which some years ago the mobile phone rate examples had?
(I thought about something like electricity tariffs, but I have the feeling that they would find it boring and not related to their real lives.)