not too many people make high output alts for that type of car. depending on what value alt you want i would to an stinger dealer and ask them about their alts. they are a little pricey but the are the best on the market.they are built from scratch and they have whats called idle performance, at idle the alt spins up to 80%. theyre rock freakin solid. also if u get a ho alt u want to get a battery too. like a stinger or svr or optima.
Unless you plan on running your system with the engine off I'd apply the price of a new battery towards a better alternator. I'm running a plain ol run of the mill stock battery with a 170 amp alternator in my Explorer with around 1000 watts rms and have no problems.
My battery starts my car. My alternator runs my system.