I like rug doctor rentals too...but you also need to buy chemicals in quantity usually needed for an entire apartment. The entire operation could easily run you $50 bucks, leave you with lots of left over chemicals, and after all is said and done, you only have a clean back seat.
That said I have a buddy who has a Bissell "Little Green" Carpet Cleaner. It is hand held, about the size of a sewing machine, and has 8-10 foot hose with a spinning brush at the end, which does everything my upright vacuum sized carpet cleaner does. Wet, chemical application, scrubbing, and sucking out the moisture. That thing has been awesome the several times I've used it.
I found a heated model for under $100 bucks at
amazon.com and you'd still have a machine to use your chemicals in after ~this~ job is done.
Very curious as to what you actually spilled?
-bear