There may be a solution there, or something close enough that it will take little modification to make it work. You may not necessarily find a _mac_ based solution, but you may find a web-based solution, for example one that uses Apache, MySQL, and is written in PHP, Python, Perl or Ruby. All of that runs on your Mac (if it's running OS X).
You can set up the Apache web server so that it serves the application pages only to the mac its running on, this makes it closed from the internet.
The developers of such a project may even be willing to take pay to customize it for your needs. Since the projects are open source, you will be able to hire someone to modify it for you, possibly at much lower cost than you fear, depending on the extent of the modifications.
