I'd say start saving now because it will likely be another year before it's out, you probably won't need more than a $500/460Euro system for it though. We can't really speculate anything accurate until it's released, but it's fairly likely you'll need a newer computer for when it does come out, as you can probably only barely run MB:W as is.
We haven't heard anything about M&B:B in a while, but this is the bet thread for it:
