I missed this when you posted but will jump in now.
The best price/performance bet is the car you already own. I would suggest upgrading the wheels/tires first. Remember a regular Civic is designed to haul people/stuff in a relatively comfortable way. The stock tire sizes are selected with this in mind. Performance tires with different size/width ratios will perform better at the expense of comfort. After that you can think about different springs/shocks/roll bars.
Engine upgrades depend on what engine your car came with. As @[email protected] said the turbo provides more options for upgrades.