SVS's business model in 'the old days' when they were building all kinds of monster subs nearly put them out of business. They were acquired by new owners who made them not just profitable but massively successful. They weren't victims of their own success, they were rescued from total failure. They have turned into a much better company than they used to be. Better engineering, more reliable products, more accessible and better availability, and ultimately more sensible overall. There are other companies that do offer a higher $/dB ratio, but what does that really matter? SVS buyers generally get the level of SPL that they want. Not everyone is after 120 dB. Most of my family and friends would never be able to accommodate a huge sub and would never be able to use it anywhere near its full potential anyway, even if they did have space for it. Keep in mind that the home audio market as we know it is shrinking, and people aren't buying as much subwoofers, AVRs, and large loudspeakers as they used to, yet SVS has been growing. Their products really do measure and perform well, as I have seen time and time again. Wait till you see the measurements for the 3000 subs...
One thing that you have to factor in the "it depends" condition is how much SPL is really desired. Some people would be just fine with two SB-2000s in a 18x27 foot room, and others would want way more SPL than two FV18s could produce in that same room. Six PB12-NSDs would be able to get you a much higher quality sound than two FV18s, btw. With placement experimenting, you probably could get a flat response without any EQing at all, which is the ideal. And the SVS system would be very close in headroom as well.