People have lots of different opinions when it comes to RCA's. Some people say "just use the cheap ones" others say "buy the best you can afford".
I think that better RCA's do make a diference. I had a bad case of alternator whine in my M3. I just upgraded to Stinger's Expert series RCA's (best they make) and the nosie is gone. Remember, you're system is only as good as it's weakest link.
I'd personally stay away from any of the big chain stores when it come to buying any kind of audio equipment or accessory. Go to a specialty audio shop...or go online. Sound domain (
www.sounddomain.com) has the expert series for $68

(ret. $150) or a 20' cable. Or get the audio shop to match the online price, that's what I did.
Hope that helps.
Trev