Developing a budget takes quite a bit of work, and you probably won't be able to do it in one sitting.  There can be many things to consider when putting together the budget for an event, however there are some larger expenses that deserve more of your attention and will have a much bigger impact on the event itself.  Below are major things to consider.

- Audio Visual

- Catering

- Decorators

- Equipment and Furniture Rentals

- Meeting/Venue Selection

- Printing Costs

- Speakers or Entertainment

- Transportation (if needed)

These are the major categories.  You can get bids for any expense no matter how minimal, however keep in mind the quality of their product or service, their ability to meet your deadlines, and their willingness to make good if there is a problem.  You should look for vendors that are recommended by someone in the industry you trust or you might try asking the venues for their suggestions on who they have worked with before and had great success with.   You only want to work with professional vendors who do events and offer event services full time, after all, you only have once chance to make a great impression and it would be a shame to ruin an event by using inexperienced vendors or part time event planners to save a little bit of money.  If you must cut costs, try to make the cuts on things that will not have a direct impact on guests or that the guests will hardly notice.  In the end, it is your name or company on the line and you want your guests to have a great experience, don't you?