Consider the importance of venue selection, including the possibility of alternatives that may seem outside the regular conference/personal event box, but could be great substitutes. One of my family members recently got married on a (permanently docked) boat in Seattle, an absolutely perfect venue (and much less expensive on a total cost basis than an upscale hotel). Other options include historic sites and landmarks. Just last week, BravoSolution held their corporate event at Café Brauer in Chicago, a Prairie-School landmark building overlooking the Lincoln Park Zoo (where many weddings are held, in fact). Let's just hope that the typical wedding guests smell better than most sourcing executives (or bloggers) from the Midwest -- or was that the lion cage wafting in ... 😉
In all seriousness, the prospect of a non-traditional venue can bring both reduced cost (not only because of venue cost, but greater flexibility on catering and alcohol requirements, such as bringing your own). It can also help to either provide as much advanced notice as possible (with flexibility in dates if priced breaks can be offered at certain times) or to wait to the very last possible minute to schedule a facility, which can introduce event risk but also significant potential savings into the equation.
A decade ago, my wife and I got married with only a few months notice (to save the mothers from killing each other but also to save a few bucks) and were able to secure a facility at a great price owing to relative last-minute availability. Whatever you do, avoid the 6-12 month window of advance booking (that's when they tend to get you the most). A final subject of venue selection is to pit venues against each other on a total cost basis, not a unit cost one, once you establish general availability on a similar date (or a substitute one you're happy with). Find one you want and have them match item for item, either directly or via a discount schedule, the package a suitable alternative is offering.
Next, don't discount the entire air travel planning thing. While it's unlikely that you'll be able to negotiate a discount with airlines directly unless you have thousands of attendees (or an airline is a sponsor of corporate event), it's still possible to save a bunch on a total cost basis, especially as your guests go. Here, it goes without saying that it's important to encourage attendees, especially those on a budget, to compare apples-to-apples total costs on tickets (e.g., factoring in baggage costs on major airlines and such in the case of non-frequent fliers). If the event is far enough out, you might also wish to consider suggesting Southwest over other airlines (if the routing works) because they're the only one that allows you to rebook a ticket without cost if the price drops which is more than an unlikely possibility, provided enough warning. With the majors (e.g., United, American, Delta), you're out of luck in saving money unless the price drops more than enough to make up for the change ticket fee.
As a final piece of advice, especially if you're considering the event for yourself, you might wish to try before you buy (especially if you're still shopping or debating about whether or not the current option in front of you is the one you want to bet your life on). In the spirit of Wedding Crashers, we like the following advice applied to personal affairs: "Attend. Don't exhibit. Key customers attend your prime shows, and you can, too. When your events marketing budget evaporates...register only as an attendee, where you can use the [event] as a networking opportunity." Just be sure, at least in the case of weddings, to have a loose definition of "networking."