we go every year (apart from missing a year when I was pregnant) for the last 12 years and we are going again in november.
Dont book through agents as they ad around £300 on top of it, go to the disney website and book directly as this is alot cheaper plus you get the opption to book some of your meals alot cheaper at the same time.
Ferry is alot cheaper but by the time you add in travle to the port and then to the park the other side you loose best part of a whole day that you could have spent in the park.
Eurostar isnt that bad a price and if booked a fair bit in advanced you can save a fair bit plus we just booked ours the other day while they had a special offer on, we got ours cheaper though by getting the train into paris rather then the park because it knocks over £100 off the price and then we just jump on the metro into the park which is only a 20 odd min ride plus you can get there alot earlier doing it that way so get extra time in the park.
But only ever do that if your confidant about what train to get on and traveling around paris, we are pretty used to it but the first time we did it years ago I was scared as hell and we got scammed (it actualy bordered on being mugged) so its not something I reccomend for a first time visit.
Dont bother about getting lunch in the park it will cost about £10- £13 per person just for burger and chips, instead get some rolls and ham from the breakfast cart for free and make yourself up some rolls, fruit and yoghurt all for free.
If you are eating at the resturants make sure you book a table as early as possible because they normaly stop letting people in about 4pm and if you go at the last minute you will often not stand a chance at getting a table.
Yes booking a hotel outside of the park is cheaper but to be honest booking either santa fa or cheyann isnt realy that expensive and it realy adds alot to the experiance and makes everything a bit easier, we have stayed at most of the hotels but cheyann is by far the best in terms of decore and price.
Christmas is the best time to go, it is so beautifull with all the fake snow and christmas trees and the lighting of the castle.
Biggest tip I can ever give though is NEVER be there on 11th novemeber, its a holiday there and the place becomes so packed you cant even move, go the week after.
Any other advice you want just ask