There is no single cost of extraction. Each oil field has its own cost. For example, in the KSA the extraction costs are around $2 per barrel, still a far cry from the recent lows of $26 per barrel. The same holds true for the US shale oil (in respect to the diversity of costs across different oil plays).
I will agree with you on the Aramco production cost, but I suspect that the production costs for the US shale oil is much higher. Aramco is producing crude incurring an expense of $2 to $10 per barrel (depending on the field). The same for US shale oil is $20 to $60, depending upon the geological formation and remoteness of the location. But you should also remember that many of the US rigs produce extremely low-quality crude such as North Dakota Sour, which are priced much below the Brent / WTI official prices.
http://money.cnn.com/2015/11/24/news/oil-prices-production-costs/
