Look for the PG Xenon X600.1 on Ebay or the guy on here selling them in the classified section. They are 1 ohm stable and you ca get them for about $200 shipped. They will produce full power from one to four ohms, so either of those subs will work. Are they DVC subs?
ETA- Most of them are showing that they produce 800 to 850 watts rms on their birth sheets.