I am sure there are more thsn one solution to your issue, but using the DateTime parse functionality you can find out the day of the week. You can find the documentation for this here https://docs.mendix.com/refguide/parse-and-format-date-function-calls and more parser patterns here https://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html
You can use a custom display pattern in the user view and incorporate this into what you would like to achieve
Maybe this already helps you to achieve what you are looking for. As far as I know there is also a learning path that might have overlap with what you would like to do :)
You should do this at the backend on the server in a microflow where you first take the current day's daynumber and compare that to the projectsettings in the runtime-tab: 'First day of the week'.
You can test this in the FunctionFiddler of mymendixdemo100-sandbox.mxapps.io
So now you know if it is a weekday or a weekendday and thus you can display the corresponding price and discount.