If you're staying in Tokyo and taking the subway out to TDR, buy your return ticket in the morning when you buy your outward ticket so you don't have to worry about it at night.
Cost - as for TDR itself, admission and food is about what you pay at the U.S. parks. As for Tokyo itself, it can vary wildly depending on where you stay and eat. I stayed in a business hotel in Koiwa that reserved some rooms for hostellers - at hostel prices. Private rooms with bath. There's also the New Koyo Hotel (very cheap but very basic) for 2,700 yen. I got a lot of meals from variety stores - you can get sandwiches and salads and stick them in your backpack if you're walking around town or hiking in the environs.
At TDR, there are lots of lovely cafeteria style eateries that serve good food (like China Voyager in Adventureland) so you don't have to eat at more expensive sit down places. DisneySeas too has a plethora of lovely cafeteria style places.
There are other tips if you have specific questions.
