DisneyGal,
DH and I are both law students, so we are always doing the budget thing!
If you are going to eat alot of Counter Service, consider joining Connections to get the meal vouchers for $11, each covers a combo meal, drink, and dessert, and can be good deals. I'm sure you've read about them here on the DIS, but if not, do a forum search or go to Mousesavers.com Don't buy them on ebay, they're really overpriced there.
The vouchers are a really good deal at Tangerine Cafe and Beaches and Cream. I would reccommend eating at Tangerine Cafe (take out in Morrocco in EPCOT) even without vouchers because the sampler platter is big enough for 2, and they have an inside, air conditioned dining area and it is not burgers and fries, so it feels like a "real meal".
Beaches and Cream is also a neat place, and with 3 of you, you may want to try the Kitchen Sink. It is $21, and you're not likely to finish it, so I wouldn't do it without a voucher. Food is okay there, not great, but the desserts are amazing!
Another good deal for budgeters is the Meal Deal at AK (Disney sells this for $10.50 and you get a combo meal, drink and coupon for a bottle of water and either a popcorn or icecream later in the day.) Best place to use it in AK is at Tusker House Resteraunt. We bought 1 deal for the two of us, and used it for a half rotissere chicken, vegetables, and mashed potatos with gravy and a drink, and then bought an extra drink for lunch- about $13 or so total. Then later in the day, we used the snack coupons for a soda and box of popcorn. This is yummy food, and you don't have to buy anything ahead of time.
For cheap eats at PI, go to Wolfgang Puck Express and split a pizza. WPE is a little high on sandwiches and stuff, but very good, and a good value if you split pizzas, which aren't much more than the price of a sandwich.
PI had a deal the last time we went there (not on our last trip)where you bought a mug/bucket type thing at the beginning of the night and got discounted refills, so if you're planning to have a drink, this may be a good deal for you. Sorry, but I've forgotten alot of the details of this one, and don't know if they still have it even.
I agree with one of the other posters, eat breakfast in your room, then have a late lunch for your main meal of the day, and a counter serivce dinner, maybe split, or snack later. I personally avoid the Disney buffets bc I don't eat enough for them to be worth it, but that's just me.
About the Mears/Rental/Towncar: mears is slow and expensive if there are more than 2 of you. Rental is really high once you had the under 25 charge. Go with a towncar, we used YourRide, that has a 30 minute stop. If you are planning on buying alcohol, ask them to stop at a liquor store instead of a grocery store. Bring snacks and stuff in your luggage (cereal bars are not as heavy as glass bottles). You can do the refillable mugs and get milk and drinks from the food ct at the AS. We also pack microwave popcorn and fruit snacks for the room.
Last thing, sorry this is long, fresh fruit is like 80 cents in the parks, so if you need a snack between breakfast and lunch, an orange or bannana is a cheap, healthy thing you can easily get in the parks.
Hope you have a great trip!