Finding the "right" date or the "best" date when you are planning an event can mean different things to different people or groups. In the past, things considered were weather, time of year, vacations, day of week.
In order to have more negotiating power with the venue that you prefer, all of the elements that were considered previously need to considered differently. For instance, your fund raising gala was always in mid October, on a Wednesday. Perhaps changing the day of the week would help. Mondays are often under utilizied for events. A Sunday could give you a better rate, but then you must be cautious that the difference in rental is not eaten up with overtime labor costs.
Can you possibly change the time of year to a shoulder season if your're going to a resort area or if it's an event in a city, consider that city's shoulder season. A beach resort may give you better rate in October, whereas a city venue would not. October in many cities is high season, but early September may have dates with negotiating power.
Changing the usual time of year and date has the potential to reduce your costs tremendously, yet you will be able to coninue to have the same quality event. THe only obstacle that you'll have to overcome will be the protests of a volunteer committee or the decision maker of an organization.
I know that these are obvious ideas to many, but are often overlooked because everyone will say, "but we always have the awards gala on the 2nd Tuesday of October!". It's our job as planners, producers and strategists to explain the strategy.
You will not only save money, but will add great value to your contribution. THis is not only Return on Event Investment, but Return on Event Planner Investment.