The best way to do it in my personal opinion is to stay on site. We're staying at the Loew's Royal Pacific and there are going to be 5 of us in the room. The room is going to cost us $359 a night, which seems like a lot till you break it down. When you stay at one of their top 3 resorts, each of you get an automatic unlimited fast pass. This still falls under the same ride restrictions such as no HP and the Forbidden Journey or Olivander's etc, as the other passes you would buy if you were buying them early or in park, but they are unlimited vs. the ones that are ride once. They are estimated to be $85 apiece. $85 x 5 = $425. Did I say above that the room was $359? YAY! So I get a room, plus unlimited fast passes for $66 LESS than if I bought them alone, plus I get the unlimited option. Also I don't have to worry about the park selling out of them before we get there since they do limit the number issued every day. Win Win Win!!!
Of course this does not include your regular ticket, parking at the hotel if needed or taxes where aplicable, but it is still a great deal and the Royal Pacific is the lowest of the 3, but I've stayed there before and it is a gorgeous hotel with beautiful rooms. Of course we have 5 at max occupancy so if you had less people, things would adjust a bit more in their favor, but the less people in a room, the less the cost of the room. If there are only 2 of you, the room rates (for the dates I put in) were $284 a night. At 2 x $85 it would be $170 worth of fast passes which would mean your room would cost an estimated $114, but $114 for a hotel room at the resort is still a pretty good deal. Hope this helps!