Dan,
Don't worry so much about wattage-you can go to GrandAuto (or similar stores) and find a 1000 watt amp for under $200.00. Don't expect it to perform like a 100 watt amp that costs $500.00. There is no standard for rating wattage in amps. As long as a manufacturer can reach a wattage amount in tests (even if it is for .001 miliseconds, and the amp bursts into flames afterwards) they can advertise it as a wattage rating. Stick with known brands, lower ratings are actually more accurate. I am running two JL 12" subs with an Alpine V12 75x2 amp. I can't get the amp level above 4 (out of 10) without blowing my trunk lid off the car. For my money Alpine V12 or MTX (not Road Thunder series) are the best amps out there.
Justin