Clearly I haven't been paying attention -- last time I looked, there was some debate about whether Grand California was available through RCI.

But, yah, even my overpriced points through BG get me DVC units cheaper than owning DVC resale would. As bnoble says, if you're flexible and/or willing to stay somewhere else if it comes to it, and especially if you can go offseason, trading into DVC is likely the cheapest way to go.
(My BG points are "overpriced" in that I have a small ownership so pay more per point in MFs. I got them resale for five bucks and transfer costs, so definitely not overpriced in that sense!)