Well in your previous post I mentioned dropping in water (because then you know you have a constant force of m*9.81). You could make a very rough windtunnel as well (hell you could just use some tubing/a box and a hair dryer) and then attach something to a Newton meter (or any other gadget that measure force) and measure the force for a constant wind (and then just swap out whatever you're blowing against and compare the relative forces). As was mentioned before the most important factor in drag will not be what the thing is made of but what its shape is (a metal cube and a jet fighter are both made of metal but experience substantially different levels of drag)