Last summer we delivered a Lagoon 50, a 50 foot catamaran, from La Rochelle France (on the Atlantic coast) through the Med to Port Said , Egypt and on to the Red Sea. On board we generally had 6 to 8 people (crew and guests). Over the years we have heard how expensive cruising in Europe is and we budgeted accordingly.
The reality? Cruising in Europe is as expensive as you want it to be. Our most expensive marina cost was 180 Euro/day with metered electric and water and WIFI charge on top of that. That was in Palma de Mallorca and we could have avoided those high prices if the owener's rep had been willing to moor a little ways out of town and reserve a space in advance. Our cheapest marina cost was 0 Euro/day. We tied up to a barge in a deserted marina in Greece. No water or electricity available. Most often we paid from 35 Euro to 60 Euro/ day. (and that was with the extra tarif for catamarans)
What we learned (and were pleasantly surprised to find out) was that it is still possible to anchor throughout Europe with only a few exceptions. We met crusiers who regularily anchored out for a week or two and then came into a marina for a day or so to top up batteries and water tanks, do laundry and provision... the usual chores.
Food costs are similar to the US and often cheaper. If you shop in local markets you can eat like a king. Eating out never cost us more than 25 Euro a person for a 3 course meal with wine. But we like to ask the locals where they eat and to try to avoid "touritsy" places when we can.
If you put solar pannels, a wind generator and a water maker on your boat, you can save yourself money by being able to avoid the expensive marinas. (We had to pay 50 Euro for water in Palma de Mallorca because we arrived on the weekend of the biggest race and all the berths were full. If we had had a water maker - which the owner refused to buy - we could have saved the money and agravation and anchored out.)
We live aboard a 30 foot boat which is currently on the Red Sea. $100/month/ft is WAY OVER any amount we've ever spent!!! But then we are modest folk