For a cheap system, a small sub in the boot with a good head unit is more than enough. My mk3 Golf has factory 6in mids in all four doors, and factory tweeters on top of the dash and in the rear door handles. While they wouldn't win any "DROP DAT BASS BRO" comps, they sound more than adequate for normal use when powered through my semi-decent Blaupunkt head unit. When coupled with a 8in 100W RMS sub in the boot, it sounds a lot more expensive than it cost me. I enjoy listening to music on it, and it has a bit of kick if I feel like turning it up.