My best friend's wedding was last summer, and her solution to the cake expense was, in my opinion, quite brilliant.
Out for display at the reception were two gorgeous cakes- the bride's and the groom's. What the average reception goer did not realize, however, was that these cakes were fake-- simple styrofoam cake-shaped boxes covered beautifully with frosting and petals.
She simply cut out a slice of styrofoam, replaced it with a slice of cake, and marked it with a petal so that she could do the cake cutting in front of everyone.
In the back room were several inexpensive sheet cakes from Sam's Club, so when the gorgeous fake cakes were wheeled back to be "cut," an easy swap was made, the sheet cake slices were wheeled out, and no one was the wiser!
Hundreds of dollars were saved this way!