I'd say stick to your budget, if need be (or around it). And find something that will be great for HT, but at better bang for the buck (under ~800).
Smaller footprint, that will not get you kicked out of the house due to WAF.
For 650.00 try one of these (136 pound subwoofer is quite beefy, and is CLEARLY built like a tank)
uses a 15" driver compared to most subs in this price range that use a 12"
http://www.edesignaudio.com/edv2/product_info.php?t=2&products_id=618
Or if you feel the need to save up some money, then once again there are better options for the bang for buck, and if you stick with that company I mentioned they have a new sub that by the numbers will dominate that plus/2 sub for a measily 300.00 more
This one -
http://www.icixsound.com/vb/showthread.php?t=44277
http://www.edesignaudio.com/edv2/product_info.php?products_id=656
On a side note, HSU is one of the best known for bang for the buck.
You can also check their b-stock, search for a HO on b-stock (you will have to email them)
for 810.00 it is a GREAT sub (WELL WORTH THE MONEY, and one of the best bang for buck subs on the market).
http://www.hsuresearch.com/products/vtf-3-ho.html
however, as stated, check their b-stock (ask to be put on the list)
http://www.hsuresearch.com/contact.html
As well, when money allows, that sub can be upgraded to produce lower FR with the simple addition of the turbo.
http://www.hsuresearch.com/products/turbo.html
NOT to many subs can claim that easy of an upgrade (when money allows)