Have you seen the space in the hatchback area of a Geo Storm? I dunno how much air a CVR 15" needs but it might be pushing it to get it in a StormI would get a Kicker Comp VR. You can get a 15" and still be in your price range. One ported 15 would sound nice.
There is a difference in the Kicker Comp and Kicker Comp VR. If you have the room, get a 12" Comp VR off the internet and put it in a ported box.box ia sealed dual 12" enclosure about 33" Lx 16"Hx16" w approx dimensions
I kinda want to stay with a 12's or 10's
But circuit city is running kicker comps for BOGO for 90 bucks for 2 of them
you would probobally need at least a foot and a half per chamber to get a good ported box. That might be a bit much. But go to your car, and find out the biggest box you can possibly fit, then we can figure out if porting them is a good idea or not.