You can really spend a lot more because the entire town is a little like las vegas designed to seperate you from money. The park tickets really turn out to be the most expensive thing. Disney is very expensive but goes down in price for longer stays. But what about Universal, Sea world, Discovery cove bush gardens? you have to do your research and make some decisions. You definitely have to set up sample budgets with different itineraries. I like the one week on premises and one week off...there is something special about staying at disney. Do some research because there are a lot of timeshares out by sea world that rent rooms and are great it the price is right. They have kitchens and bedrooms and range from cheap to expensive. Whatever you do, don't actually look at a time share whatever they offer you its not worth it. We stayed at the cypress harbour by marriot and it was paradise, but the price which was cheap when we went get very expensive.
Afer park tickets food is the next biggest expense, two weeks (or three) is a long time to eat! A car may help here as you can to to a grocery store. Bottled water at Disney is about $2.75 last time I checked. Just buying a case of water can save money. Cereal and milk can help too. There are a lot of modest restaurants off premises like fridays but still it would cost $40-$50 for a cheap dinner I think. I really recommend the character meals, and they all sell out. When I went every sit down meal at disney was sold out for the week-end. Of course this saved me a bundle, but if you come all this way , you want some of these meals.
A great place to stay if you decide on a car off premises is kissimee. Its actually the most common and run down of all the areas,(a bit of a dump) but it groww on you and there is a lot of money to be saved in accomodations and food.
Finally you will have your flights and accomodations. You can really save here if you do your homework. Start checking on sites like expedia, and then compare with lets say virgin if you like them. All airlines have one day crazy sales when business gets slow that are hit or miss, try to hit one by checking prices all the time, and try traveling different days of the week and at different times.
start thinking like this ...plan on the more expensive side. (I'll have to do this in dollars) $200.00 per day for food(you can do a lot less but this is for cushion), Probably $250 per day for park tickets(disney others are cheaper), $100-$200 per day for hotel plus your airfare. This is the higher end except for hotel which can be a lot more. Also, you probably won't go to a park every day. I think your estimate is fine but you see that you need to be a little careful. Start saving and have a good time.