Pay 99$ when the beta is over and you can publish games. Where's the doubt in that? What's the mystery?
XBLA games are not indie games, they are two different areas. Better for you to read a bit about it. Don't go mixing the two together.
And it's great that the choice was using C# as the programming language. I am studying it. This works with the PSP. I just might get a second-hand one for it.