DIY subwoofer driver suggestions

I know that this isn't a DIY site but thought I'ld ask. Considering a serious subwoofer project for a friend with dual 12" drivers. I want it expandable in that, with a possible change of plate amp, I can double up to dual identical subs. The criteria for the drivers is that they would suitable for a sealed box about 3-4 cubic ft (1.5 to 2 each and up to 3' tall) and have a correspondingly low Fs, moderate Q and rated impedance around 8 ohms. Let's say a price limit of under $200 each. Maybe 80Hz max.

What has caught my attention so far is the GR Research drivers (with or without servo), the CSS Trio12 and the Tang Band WQ-1858.