Shocks/struts control ride comfort and firmness. Springs control ride height.
Replacing your springs will allow you to lower the car. Its recommended that you change your shocks for ones designed with lowering springs or you will exponentially increase the wear on your stock shocks.
Koni makes really good kits, but you can also look into Coilovers. Racelands are a low budget coil over that work for lowering the car for street use. As long as you dont beat on the car or track it, Racelands will work well within your budget.