Okay, I have found an alternate to the 18" Mael-X driver.
The 15" AE AV15 (
LINK) is the solution. I will be used in the 3 cubic foot Dayton cabinet, and a flared 4" diameter port, 15" long. Leaving net volume around 2.5-2.6 cubic feet. The port is small - but since you are using a very low power amplifier - this is not an issue. This is geared to be an easy to build, compact size high output design with very high efficiency.
The extension will be -3 dB, about 35Hz and -6 dB at about 30Hz. These are free field. In room, -3 dB around 30Hz, -6db around 25Hz, is to be expected.
With just 100 watts RMS, in a moderate size room, corner loaded, two of these subwoofers together will produce about 115-120dB at 30Hz, and 120-125 dB at 40Hz and above.
You won't have any 20Hz response, but this is a compromise. If you want lower response, you will have to DIY the cabinets instead of using pre-fabricated units.
Total cost per sub (not including amplifier) would around $510-$540 w/shipping.
I can not recommend any of the brands you want me to; I am recommending the ideal solution for your dilema. This will allow you to have no worries on the electrical load demands in your system, and will blow away your retail subwoofers with ease, producing several times the SPL, and with lower distortion.
-Chris