We did it on a vvv tight budget a few years ago now when our DC were 9 and 6. Lovely ages to go. We booked each bit seperately.
We flew indirect. Used websites like expedia and opodo as a start point to see what flights and connections there were but ended up booking with the airline direct quoting a cheap fare found elsewhere. Kayak is brilliant for email alerts and easy yo play around with flight date and times whilst searching for the best deals.
We flew Gatwick to Houston outbound and then Houston to Orlando.Coming home we flew back via Newark New York and into London Heathrow (we got family to give us lifts to the airport so different airports was not an issue with parking).
Also - if you book flights not for exact weeks - so not Sat to Sat but maybe Tues to Weds (8 days) or (13/15 days) I found the fares could be even cheaper.
Flying indirect was not as awful as I anticipated with the kids and actually doing immigration at Houston was hell of alot quicker than doing it in Orlando. You do have to go with the attitude though that the flight and wandering around the airports is part of the holiday and not something to "get through" to get there. We found somewhere nice to eat at Houston Airport and took our time eating and then had a wander around the shops with the kids.
I booked a condo with either On The Beach - which are fab as kids are free. We chose Lake Buena Vista but International Drive is usually cheaper. Condo instead of villa as we wanted to avoid pool heating charge - communal pool at Condo, means its included in the price but it was a proper Condo - with 2 bathrooms,full kitchen etc.
We did initially hire a car to get from airport and intended to keep it for the duration of our holiday but Disney charge you to park every day and as we had free transport to Disney,Universal and Sea World from our Condo,we ditched the car after a few days. We used Disney transport and with careful planning still made it to the parks for Rope Drop (opening) every day we planned to. So do consider - condo/motel shuttles and reserach Disney transport if trying to cut costs. I ignored this before we went because everyone poo pooed the idea of not having a car in Florida and said the Disney Transport was slow etc - but we save £££ by returning the car early and using Disney Transport (free with your tickets) which we found brilliant. I think its 15 dollars a day to park as well at Disney.
Shopped around for tickets - cannot recall where we got them in the end sorry.
Insurance is important and expensive - especially if you have pre existing conditions. I spent a long time researching this as DD has a kidney condition. It did cost a fair bit but whittled the price down with alot of research from my first quote.
We found eating outside of Disney cheaper. If you are staying on International Drive then you will have lots of options. We did stock up at Walmart before dumping the car on drinks and snacks and managed to get into the parks fine(but not Aquatica) with drinks and snacks in our bags.
Also a friend recently told me she stayed in a hotel (dont know the name) across the road from DownTown Disney. She had no transport costs at all as she could walk to Downtown Disney and then get on the free Disney Transport - she said the hotel cost more than I Drive but they saved on car hire, which absorbed a good chunk of the dearer hotel.
The Dibb - is a fab website for people planning Disney trips.There are some real hardcore disney fans that have been 20 times in their life! lol But there are some good tips etc. However, you can feel by reading the threads on there that your budget holiday will be pants because they all book meals at all the different Disney hotels and restaurants,special tours and extras - we did none of this pre planned because we were on such a tight budget and Ok we don'tknow any different but we had an absolute awesome time just pleasing ourselves, although we did kind of plan what we intended to do every day.
I would recommend investing in the latest Disney World guide once booked to get the most out of your trip.It gives times and date to avoid certain things and the best time to go to them etc etc.