Hey scottmel - I'm no expert on the Med cruise (haven't done one) and have only done one
ABD. We did Bella Italia last summer and loved it. I looked at the itinerary for both trips and a few things stood out. First is the accommodations. On the cruise I would expect rooms similar to the other ships in Disney's line. Small space/cramped quarters. On an ABD the hotels were very nice with plenty of space. They put you right in the middle of the action so you can experience as much of the culture as possible. There is frequently time to explore on your own at the end of the day. You can't do this on a cruise. Next are the meals. On the cruise most meals will be on the ship but look to be all inclusive (like other Disney cruises). On the ABD there are a few OYO meals but all meals are in the country you are visiting and give you more exposure to the culture again. Next, the cruise will hit Barcelona and France and then Italy. It's a chance to see several different areas of the Mediterranean. On the Italy ABDs you are in country for the entire trip. Also, the ABDs are generally small groups (25-40) that spend the entire trip together. It makes for some good company and travel companions.
I have been on several Disney Cruises (Caribbean) and enjoy those but was looking for something different with ABD. The ABDs are very low key Disney and the guides are fantastic. For our family we really wanted to experience the culture and see as much of the country as possible. We are now headed to Greece this summer for our second ABD.
As for airfare, it can vary depending on where you are flying from. My experience (based on flight for 2 ABDs) has been that the Air department of ABDs has better prices than I could find online. When I booked airfare for both trips the ABD Air price was about 40% less than multiple sights online. For full disclosure we did fly business class. In economy the difference was about 25% less. I would expect East Coast flights to Europe to be about $1000-$1500 for coach and $2500 for business class.
Good luck with your decision. I don't think you can go wrong either way.