http://billfitzmaurice.net/autotuba.html8" $40 woofer, with 20w rms could out do your 86db. And thats the point. small wattage, no draw on the electrical, cost effective.
sure, the $40 sub will do good, but its not going to make the same sound pressure levels as my $1200 sub with 1600 RMS
13.5" 50lbs and 1600w rms sweet baby jesus. Jus sayin, for $200 total i have a sub that sounds just as good