600bucks isnt much for a complete sound system, it can be done, but he shouldnt expect anything super, you can get a lvl 4 dc sub for around 250, an amp on ebay to power it for 100 bucks (350) speakers on ebay for maybe another 150 (500) and 100 on a deck? or keep stock deck and spend 100 on a treb amp, kinda tough to do it all with 600 bucks, i kno i couldnt, lol