I know about and have used MonoDroid (I'm a part of their beta and it is awesome), but I'd like something that doesn't require an extra runtime on the phone.
Thanks for your input!
I liked Visual Studio, I was really comfortable in it, I understood it's quirks and it had a reasonably nice workflow. I didn't like Eclipse, it was weird and different and I couldn't work as productively in it. But I was _forced_ to use it for a year, I learned that Eclipse prizes the "type-to-navigate" feature, and I learned to love this.
So this next part comes from someone who has felt the Eclipse pain and genuinely enjoys both IDEs (and for the record spends all of his time now in TextMate and Terminal).
I think your idea has a bad cost / benefit ratio. Android moves quickly, the developer community and mindshare is set up in Eclipse and the tools produced within by Google and other Third Parties. I think there is probably an audience for a Visual Studio plug-in, but make no mistake, Eclispe and VS offer a similar amount of functionality, the tools that you find cumbersome on Eclipse were written by people that work in Android all day everyday. You are setting yourself up to try to make a toolset that offers feature parity with the official toolchain. You will also need to offer up tutorials and documentation so that people will use it.
I'm not saying that you shouldn't do this, I'm just saying that you should be realistic with the upfront cost of doing this and the ongoing cost, especially considering the amazing rate of progress Google is throwing at Android. I think in the long run it would probably be a lot easier to work in Eclipse, but that's from someone that's already gotten through the pain of transitioning to Eclipse.
I'd definitely pay $99, probably pay $199, but definitely wouldn't pay $499.
By the way, you might get a better sample posting this same question at http://programmers.stackexchange.com -- it's a more Microsoft-centric crowd than Hacker News.