Wow, that is a great price for that!
I bought one of the DXi124 DVC Polk subs and installed it in the parking lot and it sounds damn better then my Alpine Type R 12in did running off my Alpine MRV-M450 amp in 2 ohms!I
I tried different songs that seemed to of sucked on my Alpine and this sub did not have a single issue beating out the beats!
I punched in the TS parameters of teh DXi124 in a sub simulator... The performance in an optimal box looks pretty abysmal... The F3 is about 55Hz in a sealed box. The Polk MM1240 is better, clocking in at 45Hz. Of the several 12" subs I looked at (including a couple of JL Audios), the best sub I looked at was the $150 Dayton Audio RSS315HF-4. The F3 was 40Hz in a sealed cabinet.
I bought one and the performance was very good.