HSU and SVS are very reputable sub manufacturers. They sell direct, so are not well known by most people. Two of the STF-3s will run $1064 (holiday sale w/shipping). This is probably the best stereo-sub option available for the price that will provide good visceral impact.
For slightly less expense/impact, two STF-2s will also perform well for a stereo setup. Now if you went with a 2-sub mono setup, The SVS PB10-NSD may be the best price option.
Now for a single sub setup, the HSU VTF-3HO and SVS PB12-NSD/2 or PB12-Plus will give you great performance and visceral impact. Be warned though, these are BEASTLY subs.
http://www.hsustore.com/vtf3ho.html
http://www.svsound.com/products-sub-box.cfm