Cheapest will probably be a combination — and impossible to tell without a lot of very detailed research knowing your exact dates of travel for every single city. With your itinerary, I’d start by looking at train for France, Italy, Germany Switzerland, Netherlands. Flights to UK and Ireland — although, IMO, Eurostar, the chunnel train is much preferable to flying to get to UK. Flights to Egypt and perhaps to Spain. Flight to Greece or ferry from Italy to Greece, flight or ferry from Spain to Morocco.

Remember to add all taxes, charges for checked baggage and overweight fees, and the cost to get between city center and both airports to the ultra-cheap advertised air fares. My 5 euro flight on Air Baltic ended up costing about 75 euros — still a good deal for my itinerary, but not cheaper than the train.