$79-100/barrel shale oil is costly compared to $50/barrel light sweet crude from Saudi Arabia. However, it's downright cheap compared to $129-150+/barrel crude oil, and politically viable at roughly $70/barrel (at that point, it's cheaper to take the money currently subsidizing ethanol and use it to subsidize shale instead).
Strictly speaking, old-growth hardwood isn't meaningfully renewable, either.
Take a peek at Wikipedia's article on oil shale. Especially the economic analysis part. Even if every other nation on earth decided to forego shale oil for whatever reason, the US could tell them all to fuck themselves and profitably produce more oil from its own shale than the total that's been drilled from every well on earth since the dawn of the oil era... and then some.
When the day arrives that oil routinely costs $79+/barrel, shale mining and retort will begin with a vengeance. The ONLY reason oil companies are still holding back *right now* is the possibility that they might be allowed to do wholesale drilling in Alaska (not just within a tiny piece of ANWR, but anywhere with oil that can be profitably drilled), which would blow the economics of shale to bits for at least another 25-50 years.
The point is, oil isn't going to become permanently expensive anytime soon. When the supply of $50-70 oil begins to "dry up", there's plenty of $79-100 shale oil waiting to take its place. The environmentalists who were eagerly hoping "peak oil" would make cheap gas go away are going to be disappointed, and will have to think of some new excuse to rain on everyone's parade.
