MSRP on a SA 12 is $249, so not far off a lvl 3. Everything I think is subject to your wants and needs. Do you want a sub that handles 2k rms....or do you need a sub that handles 600 rms? Brand is somewhat irrelevant. Comparing the two price wise at msrp is stupid. No one pays that, as shown with the sa 12 at $180....$69 off retail. I am pretty sure if you call Thor or any other DC rep, you can get them much cheaper than msrp as well.
I ain't nut hugging dc, heck, I am selling my dc's to upgrade to customs. But, in the end, buy what you can afford, and what will fit the bill.