as mentioned, 2ohm
mono stable amps tend to be more expensive.
so maybe stuff like:
*alpine MRD-M500 1x500WRMS into 2ohm, RRP$799
*audison LRx1.400 1x660WRMS into 2ohm, ~$900
*mtx thunder6500D, earthquake, signat
*lanzar, (coustic)
coustic hopefully will be releasing their class D monoblocs here in australia. i noticed them on their website (in links section) and should be excellent value.
the cheaper and perhaps less effective option is to buy a 4-channel amp and bridge it into 2, to run each sub off a bridged channel. the result is likely to be less punchy and authorative, but ok none the less.
something like a coustic 481QE for ~$500 maybe ok.
good luck

------------------
/////ALPINE audison DYNAUDIO »»»morel polkaudio OPTIMA Stinger LIGHTNINGAUDIOIssues of harassment, conflict, vindictive allegations, or unfairness, personal or observed, should be reported to me via Private Messages or at [email="shiny_car@caraudioaustralia.com"]shiny_car@caraudioaustralia.com[/email]