Also with each effort, new efficiencies are found. Many of the Saudi fields are <$5 so it can go a lot lower if economies slow.
Another unintended consequence is that the falling energy prices may slow (and mask) some inflationary effects allowing this to creep up on the wizards behind the curtains of the Central Banks.
Five dollars - not any more - they need money to spread around. 20 K princes with families, every public service free, and no taxes. It has become a welfare state. They need cash flow.
They can get the oil out of the existing sites pretty cheaply, but there is no reason not to sell all they can with the new supplies available from technical advances. They can be profitable when others can't. You are right that they have lots of expenses though, lots of subsidies. So they will pump away.
Here is some other details on some of the no-longer-profitable US sites (some well over US$130):
http://www.bloomberg.com/infographics/2014-11-19/shale-profits-at-risk.html
Lowest cost of production is in Saudi Arabia due to it being so close to the surface.
The operating cost (stripping out capital expenditure) of extracting a barrel in Saudi Arabia has been estimated to be around $1-$2, and the total cost (including capital expenditure) $4-$6 a barrel.
Even with such low costs, for the oil Saudi Arabia exports to the USA, the USA makes more on taxes levied on US citizens from that oil than Saudi Arabia makes in selling it to the USA.