Last time I make copy key fob in my locksmith.
This was the cheapest option. Locksmith make only "JMA" key shaft without immobilizer.
I make myself aluminium handle.
Normaly you can not start engine this key becouse it is without immobilizer bone. But this is no problem, you can cheat immobilizer and everything will be works ok.
In my city cheapest price for make only key shaft for MB/Crossfire is about $25.
In MB/Chrysler dealer oryginal key with immobilize bone and remote control is radicilus about $380.