Don't be fooled by high watt's. Pioneer makes some drivers for under 200 that can handle 1000 watts but they sound like shit. The JL set-up is so expensive (relitvely) because JL audio makes excellent equipment. Even their low end gear produces excellent sound.
As for buying cheap gear, if you're going to invest, take the time to double your money and buy quality. And don't spend all your cash on a sub and amp, then cheap out on box, wire, and other essentials. Your system is only as good as the weakest link. I've seen guys with over a grand of audio in the trunk and they have a flimsy 12 guage wire running all the juice to drive dual 12" subs. Can you say FIRE! Also, before you drop any money into audio, might I suggest an alarm system?