We were only going to spend 3 days in the park and base tickets would have cost us $218 per person. We got 6 day non-expiring for $288 - 3 more days for $70. The longer you stay, the cheaper the per day cost.
One more great tip would be that you can add water park and more to any ticket and you get an equal number of water park visits. So, we would get 6 for our ticket that would never expire. To add this is something like $53 per ticket. Just one admission is $40 so if you go twice you are ahead of the game and if you add non-expiring, well, they are good forever. That would be 12 days of Disney fun in my example.