Just a couple of recommendations, I don't have code for you, but perhaps this might point you in a good direction.
If you can get away with saving the Excel spreadsheet in an XML format then just open it as an XML doc and query for the value. However, I suspect that you may not have that as an option.
.NET has some Office assemblies to open, manipulate, read MS Office documents, but you may have difficulty getting that to run well on a server environment.
If it is an Office 2007 document, there is an OpenXML SDK that can be used to work with Excel documents.
Finally, rather reliable method (not necessarily the most efficient) for getting data from an Excel spreadsheet is to use an OleDbConnection, OleDbDataAdaptor and query it.