Toyota key replacement?

The plastic casing on both my toyota hiace keys has broken. The dealers want a hundred quid for a new one! What a rip off I have only had it three years and gone through 2 keys, I guess they are not made to last at this price and provide a steady income for the dealers. Is there any way I can just buy a replacement casing or doeas anyone know other places it can be replaced. It contains a transponder in the casing I believe but surly this can be swapped over?