Check the Disney website first, so you'll know what tickets will cost you. That's pretty non-negotiable, although they're cheaper as part of a package (hotel/ticket combo). We like Small World Vacations and Undercover Tourist as good places to buy a package or tickets; they've often gotten us discounts of 20% or so, or gotten us bonuses thrown in at no extra cost.
Off season - and very rarely, during the "high season" of summer and school breaks - you can get the meal plan for free. If you can, grab it! Otherwise, you can eat less expensively on your own. The most expensive meal plans specify sit-down restaurants, and only during certain hours, so it can be very hard to get the reservation that you need.
Rooms off property are much less expensive. There's a lot of competition, so everyone wants your business. We've had a small suite with a full cooked breakfast buffet for less than the cheapest room on Disney property. They had a shuttle, as well. The down side is that even rooms close to the property mean an hour or more extra travel time. We once had to get a $60 cab as well, when the last hotel shuttle of the day cruised through the parking lot without stopping (and refused to return).
Rooms on property never come with breakfast, so we usually bring danish, fruit and other things that don't need refrigeration, and keep them in our All Star Resort room so we can eat as we get ready every day. We gain extra time not only because we're closer, but because Disney hotel guests get extra time in the parks every day. Plus, you're right on the Disney transportation route already. (Disney World is seriously huge - you can't imagine the size.)
Houses and condos can be great, too - check out sites like airbnb.com. We've never done that, but I know others have had good experiences that way.
Look on hotels.com to get an idea of room costs in the area. They'll have maps, too, that will give you an idea of the travel involved.
If you can, go in the spring or fall. The weather's great, and the crowds (and often, prices) are smaller.
You can look up restaurant menus & prices, merchandise and everything else online before you get there, so you can have a plan and a budget. We usually buy some T-shirts, stuffed animals and even costumes before we go, so our kids felt like they had something new and special, but weren't as tempted by all the shops. We also buy trading pins on eBay for as little as 50 cents each in lots of 25 or more, that can be traded with any cast member for any pin that they have. That way, our kids collect favorite characters etc., without us paying $8 to $15 per pin in the parks.
One thing that might seem like an expense you can do without, but we always get, is the PhotoPass CD. (Pre-ordering gets you a discount.) You'll get a digital copy of every photo the Disney photographers take, complete with special borders and character autographs, as well as a lot of the ride photos. It's cheaper than buying 3 enlargements in the parks, and you could end up with hundreds of images that you can print at anyplace you print your own photos. (They give you a copyright release so it's legal to make copies or post on social media.)
Have fun!! :) It'll be amazing.