Nothing screams I'm a douche like too much bass driving around town, in your 12 year old car. Nothing is wrong with going down the highway cruising with loud music.
If you're doing it, do it right. Don't cheap out, get something that will sound good. Take it to a proper place, and get it installed unless you know what you're doing. If you're not looking for something that bumps, it shouldn't even cost all that much for a nice sounding system.