It may look like it's only for specialty pizzas, but scroll down to the bottom. There is information for cheese, pepperoni, and sausage.
You'll probably still have to estimate for the extra toppings you get on it, but a basic large cheese pizza slice with original crust will have 290 calories.
Also, by subtracting the calories of the cheese from the pepperoni and sausage, it looks like adding either sausage or pepperoni will add about 40 calories per slice. For vegetables, just look up the caloric value online and decide from there.
Hope that helps