I can make a PHP app which will extract the data you need from the XML files (either all at once or one by one - your choice) and create CSV files which can be opened in Excel just like Excel files.
I'm a PHP & C# expert, but I can't do C# at the moment because it will take longer and I don't have access to the C# developer tools at the moment. However, if you want it to be in C#, I can do it remotely on your computer (through Team Viewer) but it will take twice as long (6-7 days total) and twice the budget.