Invoice calculator

Hey ! I’m trying to build a calculator which will give an alterable price according to checkboxes.

For example, when the user choose an option (checkbox) the price will take +50€ and if uncheck -50€. I managed to build it but I have two workflow for each checkbox is it possible to build it differently ?

Also I just use a field in current user to store the price and the thing is that the price doesn’t reset, is there a way to initialize it to 0 when the page load ?

Thanks !