There are many products available out on the Internet that are a Reservation Management/Room Inventory and Billing package. We have been using one here for a few years that is FREE and quite easy to manage. In this day and age you don't have to keep reinventing the wheel every time you want to do something that someone else already does. Any Web Site can add a "Book Now" button and redirect reservation seekers on to an active inventory management site that will handle the whole process no matter where you are in the world.
We use http://www.freetobook.com but there are many, many others.
Peace and Guidance