Why are some prices in a different currency?

Each guide sets their price in their own currency, so a grid of tours can mix francs and euros. You can pick a currency at the top of any page and we will show every price converted into it, at the day's reference rate.

That conversion is a reading aid, not the price. You are charged in the currency the guide set, which is the one shown next to every converted figure, and your bank decides the rate on the day.