Actually with technological improvements these days even flat cone subs can sound very good. These subs are tiny and still pack a punch and have had excellent reviews. They are a steal at only $70 each:
http://www.edesignaudio.com/product_info.php?cPath=1_21&products_id=106
I have a SQ vehicle running a Sony deck with quad 20 bit DA converters powered by a Mcintosh amp, Eclipse components and a Rockford sub. The combination is great for SQ and SPL.
Once I am done with my box I'll let everyone know how it turns out. So far I am planning on running an Eclipse deck, Xtant amp + US Amp (both old school quality) or newer JL Audio Slash series amps with Clif Design components and two of the Elemental subs. I am aiming for SQ that can also pack a punch at an affordable price. Don't want a pricey deck that will attract a lot of attention or a $1000-$2000 Mcintosh amp in this car.