Current Inexpensive sub that can get it done cheap

Be cautious when buying inexpensive subs as they tend to produce more distortion and the distorted 1st and 2nd order harmonics can compromise midrange sound quality

If your main speakers are ported look for a ported sub, if your mains are sealed look for a sealed box sub ... if your main speakers have steep 4th order crossover slopes look for a sub with steep 24db crossover slopes, if your main speakers have 1st order crossovers you need to look for a sub that will work with that gentler first order slope ... all this will make blending sub with mains easier

More important than the name on the box is correct room placement ... setting of crossover point ... set it to high and the sub will sound slow and muddy ... try setting crossover 1 octave above main speakers -3db point and then equalize volume of sub to match main speakers

If your looking for slam stick with a 12 incher and don't worry about the room being to small as the wave must go back and forth to complete one cycle ... so a 15 foot room could handle a 30 foot wave or 28hz note

Find a sub with low distortion specs that has similar build characteristics to your main speakers and let the shopping in your price range begin

Now can someone please explain to me why I need 3000 watts to drive a sub to 121 db @25hzs when my mains speakers play at 90 db ... TIA

Madisound has either a 10" or 12" powered subwoofer at a reasonable price. Check their website. Highly recommended.

Thanks to all who replied so far! I did fail to define my use of "inexpensive" as was pointed out. I would say suggestions in the $1000 and less would be in my range.
This sub will be used for 2 channel music only, with the cdm7's. My room is 24 x 12 with 8 foot ceiling.

Well engineered ported designs as good as sealed designs IMHO.
Each has its tradeoffs -
Sealed boxes have issues mores on an issue with standing internal standing waves being feedback to the speaker cones. Ported designs exhibit other possible (arguably) tradeoffs. I’ve heard designs of both schools that sound excellent. All rooms exhibit ‘modes’ – they just occur at differ frequencies (they all will fall into the subwoofer range). Different speaker drivers end to work better in different designs depending on several factors. A major one is the ‘Q’ of a driver. The bottom line is that the driver needs to match the box design. One is not necessarily better than the other. Room modes and reflections also occur at all other audible frequencies. There are quite a few places on the WWW that will explain how to calculate them.