Awesome to hear! I think you'll be shocked if you pick up a set of actual high performance tires. Especially the ones that are rated very highly for autocross.
How much? I wanted to find great tires but I drive too much, and the whole deal with the tpms makes a second set of wheels too expensive. I recently bought winter tires and will have to pay to have them switched twice a year.I recently switched from the stock Continental All Season tires to Michelin Pilot Super Sports. The difference in handling is amazing! Steering feel, cornering, even the ride and road noise is much better.