If you want to use .NET, I wouldn't bother with C++ .NET - it's very different to normal C++, and would be just like learning a new language. And it's more convoluted than C#.
Visual C# Express is free (
http://msdn.microsoft.com/vstudio/express/), and you get a decent GUI designer. Of course, if you already use wxWidgets, you might find something like C++ or even Python easier with the right libraries.