Since there are custom Mii cake toppers, you'd think there would be custom Xbox 360 Avatar cake toppers. There are.
Design firm Paul Pape Desgins is creating Avatars (along with sculpted Miis) based on the images users send in. Each 4.5-inch, hand-sculpted cake topper Avatar is priced at US$100. Paul explains why:
My Miis are created from molds I made, and thus their bodies and heads are poured plastic, and all I sculpt is the hair. The Avatars are so varied in their styles, that there is no way for me to mold any part of them, so I will be creating each by hand, starting from the armature up. This allows the customer to tell me if they want a specific pose, unlike the Miis, which are static.
More in the link below.
Paul Pape Designs Store [Official Site]