The OP is that guy who said he bought the Alero from his girlfriend's dad for 80 bucks.
Even if you buy some cheap *** 15s you'll still need to make/buy a box, power/speaker wires, an amp and a headunit. Go on your local craigslist and look for used stuff if you're that strapped for cash.
My Crystals bump! 350rms @ 4 ohm SVC $50 each +S&H pretty rare subs as Crystal Mobile Sound is no longer in bizzz :/ The Comp series was and still is sought after... These are the CSe 15s...