My current project (I'm doing four for the surround speakers) , that I think will be very cool and fairly economical, is use a W##GTI-series woofer with a 2425J/2426J and a two way version of the "keeper" crossovers. The crossovers really do like the 12 ohm woofer load and amazing as it sounds, the "keeper" crossovers were about 10 dB louder on the woofer than the 3110 that Grumpy brought over. (We've no idea why, and Grumpy is looking into it.) This could at least partially compensate for their inefficiency and properly ported, you'll never lack for bass.
W10GTI, W12GTI, and W15GTIs continually go for about $200, $225, and $250/each NEW on evil bay and 2425J/2426J on 2370 horns go for ~$125-$150/each. A two-way "keeper" crossover using HIGH QUALITY component (Solen/Erse/Theta by-pass caps) could be done for <~100/each. Used cabinets would be far cheaper than building cabinets and the W-series woofers can be used in a whole range of sizes. (I'm using my existing 1.4 cu ft CV cabinets for 10" 2-ways with the horns mounted externally.)
I know that the W-series were intended as automotive "subwoofers", but here is the measured response of the W10GTI in a 1.4 cu ft cabinet with just a 2" hole in the cabinet front to serve as a port. This is not bad for a very simple project! The keeper crossovers actually seem to flatten out the downslope trend making the curve even flatter.
http://audioheritage.org/vbulletin/a...6&d=1190593161