What parks are you planning to do?

As above, driving is pretty much essential in Orlando unless you're going to stay in one of the Disney/Universal hotels and get the shuttle bus to and from the parks and then willing to pay considerable amounts for taxis everyhere else. The Universal and Disney parks are quite far apart from each other and then outside of that the shopping malls and food places are also quite spread out.

Cheapeast way by far would be to get a big Villa, the larger one's sleep up to 12-15 people and from the experiences I've had in Orlando it's much more enjoyable being in one of these Villas with your own private space and pool, much more freedom. Driving is very easy on the roads out there, understand it's a pain that soneone always has to stay off the drink but in a big group could just take it in turns driving?