well if u like music, as in hearing the WORDS not just the bass the upgrade to aftermarket speakers. taking a wild guess you could get some for 100-300 depending on quality and brand name. as for the head unit, try to get a used one of here or a salvage yard maybe for 50-100??
i personally dont like the rectanglular head units that fit into every single car so if u wana get a head unit then save up for a really nice one that is like 300 or up and fits in perfectly, plus u would probualy have to get one of those housing things for the wires or w/e (frogot the name of it) .