Make Excel based application available via internet

I have an Excel based application that I license to about 20 companies. My bigger clients have had success putting the application in a terminal server environment. I would like to offer a similar option to some of my smaller clients. Ideally I would like the client to access a log-on screen via a single click which would take them to the application to after successful log-on. Excel 2010 is my preferred version. My clients are hotel management companies and individual hotels. The application is read only. The application generates data and parameter files that are specific to each hotel and management company. The application, data and parameter files will be stored on the server. Access to these data and parameter files needs to be controlled via the log-on. I for example would need access to all files. Most users would need access to one or more hotels within their hotel management company. Some users would need access to all hotels within their management company. I would probably start with around 10 users. Over the next year or two the number of users could grow to around 250. Terminal Server is my first thought, but am open to other options. I want users to be able to access the application from the internet and I want to control the application environment. I am looking for someone to help me identify a company to host the application, set it up and remain on retainer for maintenance and updates.