Stereo Upgrade for 1988 Honda Prelude Si?

I've started commuting by car recently, and have come to the realization that my audio is not up to snuff. I need new speakers for sure, and would like to be able to play MP3 CDs (i have cette only right now). I don't want to spend a ton of money on my beloved car, maybe $300 max. I can do the installation myself if necessary. Anybody out there who knows good 6 1/2" speakers, and a head unit? I don't need "boom boom" power, just a good natural range of sound. Thanks in advance!