Change to payment process button

I need someone to make minor change to payment process button. I have a registration page and when user click on "Register" button, it process payment and send me email etc. The issue is that some visitors click multiple times on the Register button without knowing that the system is processing payment. I need someone to modify the "Register" button. When a user click on Register button, the button should be deactivated during payment process and display new page with transaction details. Respond if you have Ajax experience and let me know time to complete this task.