Well if you haven't yet found it yet, there is a solution custom made for this problem called a Channel Manager. These systems are basically a central engine that you keep up to date and in turn it send the update to all the others automatically. Thereby saving you a LOAD of time.
Here are a couple of the ones on offer:
HBSi's Demand GatewayTM channel management platform connects hotel companies and distribution partners, enabling them to transmit room availability, rates, and bookings data instantaneously. This eliminates time-consuming, error-prone manual processes that disrupt the flow of commerce. As a result, both sides enhance their revenue potential.
ChannelRUSH is a web-based application that helps hoteliers manage Internet revenue channels such as OneTravel.com™, BookIt.com™, Booking.com™, Caesar-Data.com™ and many more.
ChannelDirect is a robust channel management solution that enables you to update rates, inventory and restrictions across multiple third party sites from a single, web-based platform
With ChannelDirect you can increase the number of sites you manage without increasing resources. You can manage ten sites with the same effort required to manage two!Channelmanager the online hotel front office accommodation bookings and reservation system in Tasmania Australia. Accommodation booking system provides quick book hotel, motel payment portal, automatic hotel reservations, last minute hotel booking and hotel invoices management services