Hard top or convertible? (I don't quite remember?)
Assuming it's a HT, you have a better choice of speakers. And you can mount them under the rear deck with out cutting anything and hidden by the rear package tray cover etc...
Another popular "fix" for many especially vert owners is the 6x9 speaker boxes that you can set on the back seat when driving and using them, and unplug and put in the trunk when your not using them (or on the floor etc) You just have the speaker wires easily acessable to plug them in again.
In a vert... with out getting creative and with out modifying anything... it get's a little more dificult.
eBay is where I've scored on some great car stereo components. Do your home works, know what your looking for and be patient. You'll get some GREAT deals that way!
With out doing much more to your system, I'd suggest just a set of 6x9's. You can add more to compliment them later, but they will be about as good as it gets with just a stock radio... but still look for great quality at a good price rather than just something at a great price. You'll be happier!