Cruise line:
Disney is great, but we probably won't do it again -- it's just too expensive. You can almost have two cruises on another line for the cost of one on Disney. Affordable, family-friendly mainstream lines are
Royal Caribbean, Princess, and Carnival.
No matter what line you choose, be sure you're comparing similar ships. The newer, larger ships offer more amenities, so it's natural that they'd cost more. Many people say that Carnival is cheaper, but I haven't found this to be true consistantly -- especially not if you're comparing their newest, nicest ships with the other company's newest, nicest ships.
Itinerary:
I know you said that Europe'd be ideal, but the Caribbean is going to be cheaper (don't know just how important this is to you). The cheapest cruise'll be one with a port city to which you can drive.
When to book:
Pick out what you want, and book the very day that your cruise dates become available. Why? All rooms aren't equal, yet the room with the over-sized balcony and the one squeezed between the ship's laundry and the disco cost the same price. By booking early, you get the better room. Then watch. IF the price goes down, you can call in and ask for a price match; personally, I've only failed to get a price drop twice: Once was my first cruise, when I didn't know to watch, and the other was a holiday cruise. Check "up and down a category" too. For example, once I reserved us THREE connecting ocean-view rooms (4 teens in one, me and DH in the other)and was happy enough with them . . . 'til they had a great price drop, and I was able to move us to THREE balcony cabins . . . for less money. By booking well ahead, you stand a better chance of getting a great price and a great room -- as long as you don't mind checking every day.
At some point you may reach a line in the sand when the cruise line'll say, "No more. We're only 2 months from the cruise date. We're having a fire sale on our leftover rooms, and we will no longer do price matches." So what? At that point, all the good cabins'll be gone anyway. It's rare to get a really prime cabin just before sale date. It's more likely that the balconies could all be sold out, or the entire cruise could be sold out.
With whom to book?
For our first cruise we booked with
AAA. Now we book directly with the cruise line. Why? Because if I see a price drop, I want to be able to call in myself right away. And I want my cruise documents to come directly to me. I don't want to have to go through a middle-man for my vacation details.
Some travel agents offer nice gifts; for example, they might pay your tips for you or might give you a night at a specialty restaurant. I personally haven't found these deals (I just hear about them on Cruise Critic), but I still value being in charge of my own details.
Total cost:
Be sure you're not looking JUST at the cruise cost; this is not a complete cost. Include in your budget: Transportation, a night-before hotel (experienced cruisers'll say you should always arrive the night before so you'll have almost no risk of missing the ship), meals on the road. Do you already have passports or other documentation that'll get you on the ship/back into America? Onboard you really can spend as much /as little as you like, and you can have a good time either way. People typically spend on alcoholic beverages, soda packages for the kids, the casino, the spa, and upcharge restaurants. Same thing for shore trips: You can just get off the ship and walk around in port, seeing free things and stopping in the shops, or you can spend big bucks on an excursion; you can save money by doing private excursions rather than the ones offered by the ship. The one thing you
must pay onboard is tips to the staff who take care of you; this is their salary. And consider cruise insurance; I personally have used mine. It made a horrible situation a little more tolerable.
This may lead to another question: What's free (or, more accurately, included in the ticket price) onboard? Pools, sports activities, movies, meals in the buffet or the main dining room or via room service, evening entertainment, dance clubs. You'll get a newspaper on your bed every night that'll list the next day's choices.