Why are some prices in a different currency?

Because each guide prices their tours in the currency they are paid in, so a list of tours can mix francs, euros and pounds. Prices are shown as the guide set them; nothing is converted for display.

You are charged in the currency shown next to the price, and your bank converts it at its own rate on the day. If you pay a deposit here and the rest to the guide in person, the amount still to pay is shown in that same currency.