If those waterfall plots were up for auction I'd expect them to get that much. But I think they're guild plots so won't be auctioned until after everything else.
I wouldn't be surprised to see the lairs in the middle of Dralk and Chiconis to get at least tens of gold. Mere mortal dragons will have to live in the 'burbs.
But I also expect many MANY plots to not be bid on at all. If you're not too picky you can probably pick one up for about half a gold.