What is the proprietary db and how are the data tables stored (i.e. betrieve)? There's usually a way to convert almost anything providing you have the right tool for the job. I've converted several different types of data systems. You can usually find a few companies specializing in this or you can also find a few freelancers out there who'll do the job a little bit cheaper. Depending on how many tables there are and the current structure and if you want it normalized/changed in some way is where the price usually comes into play. Can you get to the actual data tables or are they locked behind the scenes? I had one instance where I had to go back to the developers of the application to design an export routine to get the tables in a manageable/importable state. Plus there's also the front-end design.
Expert Database Programming
MSAccess since 1.0, SQL Server since 6.5, Visual Basic (5.0, 6.0)