I have a 97 Mazda Miata and want to make it faster. I dont have enough money for a super/turbocharger and dont want NOS. I need cheaper upgrades under $500 per part like a $200 cold air intake or $30 spark plugs. I was also wondering about Those electric Superchargers and if they work. also please provide good websites to buy these items THANKS.

BTW its an automatic =[