your best bet to find an amp around 600 watts is to go to a pawn shop and try to find a used one thats in good shape, or id look on ebay. You could get a kenwood thats 550 watts RMS and 1100 peak for about 160. the model is KAC-8152D. I know kenwood isnt top of the line in amps, for for your money situation, i dont know how much better you can do. you could also consider if your that low on money, you could just get 3 comps, and put the extra 90$ or so toward an amp, and you could get a real nice 500 or 600 watt amp. id say a memphis PRD500.1 or a kicker KX600.1. both of those on ebay, you can get brand new for 225-250. i would think 3 comps on good amp will be better than 4 on a sub par 150$ amp.