(Not sure where I should post this. I did not see a forum sub category where you can post questions about what software / development solution to use. Each sub category seems to be about a specific tool rather than one for asking about which tool to use.)
The company I work for currently has no licenses for any GIS software. We have a VB.NET windows form application that imports a bunch of data each day, included in that are addresses (usually about 600 a day). For each address that has a different zip code from one of our office locations, we need to calculate the driving distance for each to our nearest office (not linear distance, but driving distance, so it takes into account the road networks).
What software product(s) would we need to purchase in order to implement this functionality using an ESRI solution with our VB.NET windows application? We are looking for the most cost-effective product bearing in mind we will not be needing any other GIS functionality.