This centerpiece is easy to duplicate and cheap so that no matter how many tables you need to decorate, you don't end up breaking the bank.

Step 1: The Container

I didn't want to use glass because its cost multiplies too fast. So, I used clear plastic 18 oz cups. I decided to melt the cups over a candle to make a groove all around the top just below the rim. It's a fairly fast process so you have to keep turning the cup around and around until the groove is deep enough without making a hole.

Step 2: Covering the Container

I used Ikea dinner napkins to cover the cups. They are the right size, come in variety of colors and have pretty embossing all around the sides. Plus, they're cheap.
Open up the napkin, put you cup in the middle and wrap the napkin around the cup and adjust the gather. When you are satisfied, pull up a rubber band from the bottom up to the groove.

Step 3: Adding Flowers

Now you can add silk flowers according to your theme. Our theme was pink and green so the pink carnations with greenery worked well. I put a few rocks at the bottom first so that the arrangement wouldn't be wobbly.
For cost effectiveness, I bought bought used silk flowers at a half price sale at the local used stuff shop. They are cheap and usually in great shape. You can add fresh flowers as well, of course.

Step 4: Base of Centerpiece

To make the arrangement look complete, I added a paper doily to the base. I hot glued mine in place so that I could just pick up the arrangement and set it on the tables without having to do anything else in a time crunch. I also hot glued a few petals to the doilies.
The doilies cost $1/40 at dollar stores. The petals are a whole bunch for $1 there also.

And there you have it; a simple and cheap but pretty centerpiece!