assuming you own or have access to a 3d printer material costs depend to a good part on your printing skills. After a few years of printing I still have around 30% failures in printing parts.
You will need about 4kg of material for the « good » parts. This however is only a fraction of the total costs, think of a pc, arduinos, cables or nervo boards, servos and many tools and parts (soldering iron, clamps, connectors, crimp tool, glue, tendons, etc. etc)