Convert MSExcel proforma to web based app

I have a pretty simple MSExcel proform a spreadsheet that accepts 'assumptions' typed in from the user as inputs, and then calculates and presents a pro-forma spreadsheet and a graph to the user.? I would like to convert this to a web-based application where the user pays an annual fee to have access to the application and the user could save their user sessions into a basic database.? I have a windows based server environment.? I prefer doing this with Flash/Flex but am open to other programming languages.? A free DB like MYSQl would probably be best. PLease describe your solution with your bid and include timeline and deadline dates.