Cheap? No.
But there are ways to keep costs down.
If you can go out of the school holidays, flights will be cheaper. Or consider going indirect. Try skyscanner or netflights. Or Norwegian Airlines can be good for direct flights.
Look on Homeaway or Holiday Lettings for self catering accommodation.
Stock up at Walmart and mostly eat in, buy snacks and drinks to take to the parks to avoid paying for meals while in the parks. Most parks will let you take food in, but generally portions should individual size, so no big bags of crisps, party subs etc
If you don't want to cook in the evening, order in takeaway pizza (very cheap compared to here), buy in salads/chicken etc from Walmart, or find buffet-style restaurants (we liked Sweet Tomatoes)
If you prefer a hotel, generally off site is cheaper than on site, some may offer free shuttles to the parks, and if they include breakfast, you can fill up before you go out for the day.
There are shops that buy unexpired tickets and sell them on - look like beach tahirt shops
The tickets will be a major expense, but I wouldn't recommend buying unexpired ones. As far as I'm aware, these are illegal, and are likely to be a scam.