Checking airline rates prior to a cruise is a great idea. No tackiness, just a wise travelling strategy. I would check both airfare and cruise rates and find the "happy middle" that suits your timeframe/budget.
Ryan air is great, for travel WITHIN Europe. Although their baggage rules etc are very stringent. I have found drive to be cheaper for travel with 4-6hrs of driving distance, but I own a car here so rental rates may make or break that idea.
My mom recent flew to germany to visit from Fl. She flew United for about $1,200. Thats an excellent price from what I've seen from searching for similar flights. Most travel sites have comparable fares, sometimes the airline sites have better prices though.
Any flight around $1k is a decent rate. Flying into Cruise ports seem to have higher rates, conveniently enough. You may want to consider flying into a "cheaper" city then taking the rail system (which can be considerably faster or much slower than car travel depending on the train type, regional versus ICE) or getting a bus transfer.
Also note: the euro to dollar rate right now is HORRIBLE (1 EUR = 1.41564 USD).
Keep this in mind if you look on europe based airline/travel sites.
I hope this helps. Good luck.
BTW- I am taking a cruise 10 Sept leaving from Italy. I found driving 8hrs each way and paying for the port parking was cheaper than flying on any airline, to include ryanair, and allowed me more travel flexibility.