$3-4K is a lot of money that can also go really quick if you don't have a plan.
 
	A few questions to help guide the process.
 
	
		Do you plan on doing the work yourself?
		
			
				Are you willing to learn the details of RMS vs peak power to help build a quality system
			
			
				Are  you comfortable with removing panels off your car?
			
			
				Are you comfortable with tools in order to build a quality subwoofer box?
			
			
				If not, do you have a friend that has previously put together systems that would be willing to help?
			
			
				If not, you will probably need to find a reputable shop. Understandably, your $3-4K won't stretch as far due to the cost of labor.
			
		
	
	
		What are your real goals?
		
			
				Listen to high quality music?
			
			
				Impressive friends with a rattling trunk?
			
			
				Do you want to maintain trunk space?
			
			
				Reduce road noise to increase your music experience?
			
			
				Just be loud?
			
		
	
	
		Any reason why you specifically want 2 12's?