How can we divide the price if the customer select certain attributes? I am working on a magazine site where the magazine can be subscribed. When users subscribe, we want to allow them to choose between full payment and monthly payment. I have used a "payment_type" attribute for the payment option, and I want to divide the total price by the number of months when user selects the monthly payment option.  

How can I achieve this?
Why dont you try the Rules module? It is great for that kind of automation.