I am in the middle of a similar migration, except we chose to end with a .net front end application instead of a web based.
What we chose to do was to migrate first migrate the business logic out of the Access front end, and rewrite it in C#. It took a while, but we eventually got most of the business logic switched over while keeping the same front end. Once the forms were reduced to visual display, we started moving sections of the application to a .net application. We are now in the final stages of deploying our application as a full .net app with no dependencies on MS Access.
I have worked on a number of significant "Legacy to current" types of conversions over the years. The most successful ones were those that migrated functionality to the new platform at a measured rate.