Heres what I would suggest, coming from a guy who runs pretty cheap.
Get a couple sets of decent Sonys for say 70 dollars a set, a cheap 12 inch, alpine would do just fine for that (and an amp to go with it ofcourse), then pick up a small amp to power a couple of the speakers, or a 4 channel amp if you can find a decent one. That amp is going to infuse your speakers with some distorting bass, so you'll want bass blockers for the speakers, so that you can still turn your sub bass up without turning the speaker bass up as well. That is, ofcourse, if the headunit doesn't already have the tuning capabilities for that, But I have a pioneer and it doesn't. With all this your going to need the wiring. Some 12 guage for the sub and 16 for the speakers wouldn't be bad.
Anyway, I know this is all pretty cheap stuff, and its not high class or anything, but for the average street car this will be plenty loud, I promise. Remember to 'break in' your speakers and sub, dont let your girl blast it right out of the box or the speakers wont last as long if shes planning on cranking it all the time.