The first and most important step is to have a centerpiece budget, preferably a per table cost because it's an easy way to keep track of your numbers. The number of tables is bound to change as people are added and removed from the guest list, just make sure there is a bit of extra room in your budget to accommodate for this. Any extra centerpieces you may have can be used for the cake or guest book tables and then given to special guests at the end of the festivities.
You don't have to know what you want your centerpieces to look like yet, determine your budget based on what you can afford and what you want to spend. Come up with a reasonable amount, say $10 per table and build that into your overall wedding budget. Play with the numbers until the bottom line works with your financial resources.
If your budget doesn't have room for centerpieces once all the necessities are factored in, consider having centerpieces that aren't to be taken home by your guests. Some halls have table decorations that can be used, often for a small charge. It may be an option worth looking into.
Once your budget is set you will need to stick by it. Now is not the time to be impulse buying if you happen to find something that is just irresistible, even though there will be plenty of opportunities to do so! There will be enough unexpected expenses as it is that will wreak havoc on your budget, don't let your centerpieces be one of them. With some careful planning you'll be able to put together great ideas that are within your budget.
