Basically I know some bit about speakers and have read a couple things on what makes the speakers better. What changes in the inside of a speaker makes it sound better. In this case i am wondering about subwoofers. Ex: What change in the build of the speaker makes it have a higher sensitivity or lower frequency? In my viewpoint it doesnt seem like it would cost so much more to manufacture the higher quality speakers.
Essentially, all the parts working together are elements that impact the sound quality. In addition, the precision of the assembly is very important and can be very expensive. Price doesn't always reflect quality (as it just about everything), but generally, exotic, super stiff cone materials, strong magnets, precision wound coils, careful assembly, etc. drive up material and production costs.
The part that makes most of the sound is the cone, having a stiff cone is important, but it also needs to be light, the part that moves the cone is the coil and the magnet, having the coil would regularly and withstand the power that's put into it and the magnet have sufficient strength are also important, the flexible parts at the edge and around the coil keep the cone lined up and the coil moving freely between the magnet pole-pieces,the frame holds it all together and should be rigid enough to keep it that way given the usual abuse it will see being shipped to the customer, fumbled by it new owner, and relocated by roadies etc.