I've gone 3 times as an adult so far (once about every 3 years, so lots of time to save) and as we have very long trips (7-8 days) the hotel is the most expensive by far, but only because as we go rarely, and we opt for the Grand Californian Downtown Disney view. So multiple thousands of dollars for that. But if we chose to stay at, say, HOJO or a like hotel, it would only cost $1300 for the entire weeklong stay!
Airfare from Maine to California RT is around $1200 ( if you're REALLY lucky!) to $2000. I always get either Southwest or Jetblue so I get some free checked baggage.
Ticket price REALLY stinks ever since they got rid of the extension options past 5 days. For my family of 4 to go 7 days it goes somewhere around $1800!! Needless to say, when we move to CA we're getting annual passes! Much more cost efficient.
Finally, FOOD and ITEMS... I budgeted $150 per day for my family of 4 last trip, and had difficulty staying within that amount. We would often get one "sit down" or character meal a day, and the rest was whatever we felt like grabbing. This ALONE was almost our entire budget for the day! So any items we wanted took up over-budget. Next time aiming for $250 a day if possible. I'm sure this is lower for families who are more savvy with their food, but as we don't go very often, we only wanted to try all the different Disney fare and character meal experiences
As for extra costs, I'll budget a little for "arrival goodies" for the kids at the hotel (they love the little pirate cake and balloons!) and will get Disney pajamas from Disneystore.com ahead of time for the kids (much cheaper online). Also the transportation on the Disney bus was around $100 RT from LAX. Next time I might splurge a bit more for a private towncar, as if you stay at GCH the bus will first stop at DLH, where you get out, get your luggage, then get put an ANOTHER bus just to go next door. Quite the hassle!