Yeah what plinkie is saying is 3 Variables
Everytime you gain points make it add to both Score and Score2. Then make a seperate event When Score2 is equal or greater to 30,000 subtract 30,000 and add 1 to Lives. That way Score2 will always be somewhere between 0 and 30,000 but the main Score variable is always increasing and indicative of your total Score :)