Inductors are usually just a coil of copper wire, sometimes hundreds of feet long. Copper is the only realistic material to use. One way to lower resistance is to use thicker wire. You can purchase a more expensive coil that uses a heavy gauge wire. Moving from 19g to 14g increases the price by at least 5x's. Using silver increases the cost another 20x's. There are also copper foil inductors which are more expensive, but work somewhat better. Some inductors have iron or ferrite cores in the middle of the coil. This core decreases the amount of copper wire needed for the coil, and therefore lowers the resistance. The problem is that these cores cause some distortion. For smaller inductors, use one without a core - an air core inductor. For the larger inductors required for the woofer's crossover, an air core inductor might not be feasible. In these cases, use a ferrite core. If you want to try to make your own inductor to save money, check out the Inductor Calculator for information on winding your own coils. I hope this helps...
