Are you paying for the dining plan? If so, drop that and go with a value resort. That will make the initial bill cheaper.
Then you'll have the options of dining where you please, and can keep costs under control by using the many (very nice) counter service restaurants.
If you are determining your costs hoping for free dining program, remember that it's not truly free as you are paying more for the room.
The less expensive times of the year are those periods before and after major holidays and spring break. Easter, Fourth of July, Thanksgiving, and of course, Christmas are the times of the year things are most costly, with Christmas being the very most expensive time.
January is less expensive (marathon time, though). Parts of February and March can be depending upon spring breaks and Easter, same for parts of April.
May and parts of June are less expensive as most schools, colleges and unis are still in session.
September and October and part of November see it less expensive, and the first week or two of December...