My opinion is I love my Tempest, and at $150 retail it's very good. I don't know if you can find a better $150 retail subwoofer. Especially Audiobahn. However, I purchased one of their low-end 12" subs off eBay for $50 and it was decent for the $50.
1999 SE White
AVH-P6500DVD
Infinity Reference 6500CS
Pioneer 5x7s
Punch 360a2
Punch 500a2
Adire Tempest in a custom sealed 3.4cuft box
Modded Xbox
Still need Midnight Cloth Headrests... and if somebody has fold down rear seats....