What is the most cost-effective material for prototyping a drone airframe?

[Jarfi]

I am designing a drone airframe, what is the best, simplest and cheapest material to make a prototype? Is Polyurethane foam a good option for the body?

 

[Simon Bridge]

Congrats.
To make that sort decision, you should work out what you need the airframe to do - i.e. what sort of stresses do you need it to be able to withstand?

The cheapest material would probably be lightweight balsa struts and cellophane, but that is probably going to be too flimsy for you. You can get various types of resin cheaply but it may be too heavy. Polystyrene is certainly very cheap - you can often get huge blocks of the stuff free at a recycling center. But without knowing the parameters of your design needs, it is not possible to answer your question.

Balancing the material needs of the project is part of the skill you learn becoming an engineer.
You will want your drone to fly (maybe not - maybe it is a wind-tunnel mock-up?) so how high? How fast? What sort of accelerations do you expect? All this affects the design.

 

[satchurated]

Polymers are cheap, but you will need a stamp and someone for the hot forming. Balsa is cheap and easy to handle, but weak and the torque of motors will twist the arms of your quad or hexa...in the market you can find arms of plastic or carbon fiber kits..is up to your pocket