Until you've autocrossed for awhile, don't worry about the car or its class.
It's ALL driver. Invest in some decent tires and go to every autocross you can. Ask questions, ask for rides, heck, ask veterans to drive your car (if you want them too).
I'd love to blow all my money and make my car no longer stock (which will happen eventually
), but I know I've got a long way to go to become a better driver.