Before spending hundreds or more on a presentation cake...take a few "FAKE CAKE" tips from me.  These cakes can be decorated boxes, covered Styrofoam disks or just plain cakes from a big box store like Sams.  The key is to fool the eye. That technique is call trompe i'oeil.  Have the display cake as a centerpiece and have the sheet cake already cut and ready to serve on plates.  A back section of the display cake can have a real slice inside for pictures.  Nobody know, or cares.  Trust me!