Personally I'd just throw it into a number of SQL Lite table and run Linq to it via EF. Or just write SQL against it. Pretty much just text files. If it were

Personally I'd just throw it into a number of SQL Lite table and run Linq to it via EF. Or just write SQL against it. Pretty much just text files. If it were too big (probably not if Excel can handle it) I could also just load up the data into memory via a TSV/CSV deserializer, of which there are a few for .NET. If it comes as excel from the source, excel extraction is a piece of cake these days (the codebase I work on takes excel as raw input for data feeds). As for nothing else letting you build/change/copy/paste data into a table, Sublime Text Advanced CSV package is fantastic for editing tabular data, and Sublime Text has no problem handling files many gigabytes in size.