I have a 2000...not sure how different it is...but I fiberglassed a sealed box into the factory sub location (I didn't have the factory sub, though, since its optional). The box I made replaced the cargo pocket in the rightside rear interior panel. It's about .5 cubic foot. I managed to squeeze an Elemental Designs 11.kv in there (which works well in that size space). I'm running it off an Alpine PDX, which I hid in the bottom of the center console. The system is really stealth and factory looking, but packs a punch considering it is not visually noticeable and took up virtually no space.
If you are planning on paying to have someone do this kind of work, expect to pay a ton for fabrication and installation.
If you do it yourself, you will pay about 1/3 of the price overall, but you will spend hours and hours (depending on your skills) getting it right and finished. It's definetly not a task for those with limited time or capabilities.
Another option would be an MTX Thunderform, JL Stealthbox, or a Q-Logic box. One of these companies must have a vehicle-specific box for your needs.
If you have any other questions, let me know. I can recommend products or even show you some pics of my project to help. Good luck!