Don't hire a car and get staples for breakfast, snacks and water for the parks for a website like Garden Grocer (I use them, they are so good) Value are great places to stay and the poster who mentioned kids meals is right, I've done it and they are a decent size, plus you get a drink and a small desert. However, the only offer with Values is a free breakfast, not a full
DDP (at least in the UK, it may be different over there, if you can get it then that is worth going for, but, don't buy it otherwise if you want to budget)It's fine if you can find someone to share off site with and have a car, but, you would have to be on the same page with going to the parks or one of you will be doing extra travelling if you park at Epcot and one of you wants to go to MK, plus the cost of parking too. I would stick to being on site, even if sharing.
I hope it all works out, I did the 'see if you can do it on a budget trip' in May and it was brilliant, I used my
Virgin Atlantic points for the flights ( I had to pay $350 in taxes grrr, but, the flights were free) stayed at Pop Century and bought a load of groceries from Garden Grocer, I made sandwiches for the park everyday for lunch with chips and things like boxes of Craisens for snacks (I still had my ice cream treats, so I didn't do without)and my own water which I had in the fridge so kept everything cool as they were like little ice packs and saved so much money.
Just keep doing the homework and look at sites like Expedia and use those cashback and reward sites, I used one for my hotel and got £120 back as a cash reward and I did this just 8 weeks out, so you have plenty of time to plan. Good luck!