In that case, I agree with mike c. 2x $750. I think that's the point at which you get some grown-up infrasonic extension, but you probably don't need the SPL of, say, a Reaction Audio Echo 18. And having two will let you smooth out the response for a wider seating area.
http://www.hsuresearch.com/products/vtf-3mk5HPDual.html would be at the top of my list I think.
But, I have no problem with Room EQ Wizard, time-aligning multiple subs, and using a MiniDSP. Your mileage may vary. A single sub would certainly be a lot simpler! And that's an important consideration. Do you intend to use your AVR's bass management? If so, does your AVR have independent correction for dual subs, perhaps Audyssey XT32 + SubEQ HT? If you answered "yes" then "no", then go for the single sub.