Basic OEM Audio Upgrade Recommendation?

what is "heavy money" $500.00, $250.00, $700.00 ?? I think for that many miles you are driving I would recommend to you a Alpine CDA-9847 head unit. Its pretty affordable at $200.00 and allows direct connection for both i-pod (using the KCA-420i $100.00) and or your satellite radio to instead of fm modulation.  The head unit will allow you to expand and will right out of the box sound 3x the price you paid for it. Even with those OEM paper dual cone speakers. From there I would look for a small 4 channel amp if you have not blown the factory spkrs. You can find one used on E-Bay or a friend who needs cash. I believe that you could put together a pretty decent system for about $700.00 give or take a couple of bucks. But it would more than pay for itself if you are in the saddle for 150 miles each day! Man thats some drive!!  good luck.  Oh yeah for seprates listen to Diamond Audio's D361 componets or Alpine SPS-171A Componets. Front only. Rear fill can be accomplished by OEMs but get an amp to get the full potential..... mark