Forget the RE XXX. Right now you can get TC Sounds LMS Ultra subs for really low price (well, low price for a LMS) from Sound Splinter. 12" is about $450, and 15" is around $550. Give or take a few $$. The modern version RE XXX is a superb driver - but nothing is superior to LMS currently. They have the most linear motor systems in the world; absolute flat BL from rest to x-max. The Sound Splinter RL-S are what you want(these are simply re-badged TC Sounds LMS Ultras with some customized TS specs and cosmetics), they have 12" and 15" availalbe right now, and these versions have 38 mm one way linear x-max, 50mm one way mechanical limit(x-mech). You ideally want to use 2000 watts RMS or more for this driver. But 1000 RMS will work well for a ported system, or a sealed system where no LF 'boost' is used.
Sound Splinter's re-badged LMS Ultra 15":
-Chris