I have a single JBL GTO1214D 12" sub in a box in my trunk. It's powered by a JBL GTO3501 amp. Recently the sub seemed to be shorting out and would work and then stop. If I push on the sub, it will start working again and the audio place said it was going out (I think he said the voice coils were hanging up.). Before I go out and spend $140 on another identical sub, I was wondering if there would be any better sub options around the same price.
Check out fi's lineup of X and SSD's they are excellent for lower power alternatives. Though I run over twice what my SSD18's are rated for no problem. (3600 RMS to two rated for 1600 RMS) Even with very little power, they sound great and get loud too, I remember being able to pull hairtricks with only a couple hundred watts to the pair! FI CAR AUDIO
There is also some very good subs from many other companies out there, but I end up buying fi for 99% of my projects and for my customers installs as well.