The price for Disney cruises depends on the destination and time of year. Generally, a three day cruise is between $400 and $1000 depending of the type of cabin you want. A longer cruise can be up to $3000.
If you travel in the summer, you're going to have to pay the highest price, in the high season. You only have to pay for the room though, and not how many people are in there.
Any travel place can give you a very good price on a Disney cruise. Disney has made many special offers available to any one who wishes to go on a cruise with them.
Yes, you can compare prices for Disney cruises. The prices will vary based on time of travel and type of cabin booked. You can compare prices online and through a travel agent.