It's practically impossible to get any meaningful discount on Park Admissions. If you are really looking to save then:
1: Parks are in two groups - call them Disney and not-Disney. Each group has separate composite admission deals. The "both" offer above is more or less simply an addition of the two. If you can decide to spend your time wholly in one group or the other then that will save close to 50% on your admission costs. Both groups offer longer period passes (eg two weeks) for pretty much the same rate as 5 or 7 days. Which to choose depends on your own likings and you can get a pretty good idea of who has what on the web.
2: Car hire and insurance and (esp) parking costs a minimum of about £300. If you can bear to spend a longer time travelling, then you can access all the attractions for $16 each per week (say £10) by bus. As long as you stay on a bus route. So - saving close to £300. You won't be going to the coast by this method, though, but you can get to the major shopping locations and places to eat, etc.
3: Look at separate flight costs and watch for sales. And look at hotel costs separately, Add together and compare to any package you might see. There isn't a hard and fast rule here - it all depends on who is offering what. But it's often the case that indirect flights (i.e. where you transfer at some big US city) work out cheaper than direct ones.
4: Don't be taken in by low headline prices for flights from eg Thomson or other charter/holiday firms. It's often the case that such flights carry many extra fees for e.g. a sensible luggage allowance, onboard drink, and some fly into a distant airport, Sanford, and that consequently costs more to get to the resort/attraction area - if by taxi, add about $120 round trip over the cost from the much closer Orlando International. (You can even ride the bus from the latter and save a bit more). Add up the true full cost including any such extras before booking. You may well find it totals out much closer than at first sight.
5: Kissimmee has probably the cheapest hotels, but is a dreadful trip by bus for Universal, Sea World etc. It's good enough for Disney, but stay on the more easterly secion of US192 if you need this. And only stay here if, of the two "groups" you pick Disney over the rest. Otherwise, head for International Drive. In hotel terms the "you get what you pay for" is largely true.
6: Breakfast. Assuming you do want this - by the time you have added a juice and hot drink to your cheap "all you can eat" buffet, you are in for upwards of $10 pp daily, so $200 on your 10-day trip. More if you want a-la-carte, even in Dennys (which IS good, by the way). Whereas, if you choose a hotel that has a "free" breakfast offering, whilst the choice may not be as great, it nevertheless works well enough and saves you that $200. Plus you can help yourself to drinks, too - often outside breakfast hours. For cheapness in this context, look at Holiday Inn Express (note: has to be "Express" - normal HIs don't have a free breakfast); Hampton Inn, Extended Stay Deluxe, all of which are reasonably priced and on International Drive. Extended Stay has a full kitchen in each room so, for even greater savings, shop at the supermarket and eat in occasionally.
7: To save around 5%* on your in-resort expenditure, get a fee-free credit card from one of these:
Top credit cards for spending abroad - Money Saving Expert and use it utterly everywhere you can. Keep all but around $200 of your spending money safe in your bank at home, ready to pay off that card account in full two weeks after it lands. Don't be tempted to spend more than you can afford.
* Approximate and average. Rates vary daily; if the £ rises between now and when you travel, this will be a greater saving. Conversely, if it plummets, it won't. As this is wholly unpredictable, it's a complete gamble whichever way to play it, so you can only judge it on averages.
HTH