It's not so much the cost of extraction that's involved in setting the price, it's the price needed for the producers to balance their budgets.
Crude oil is a traded commodity, the price is set by the market according to perceived supply and demand. The reason for the fall at the moment is as the early post stated related to the US production. Around 2007 the US only produced about 30% of its required oil with about 10million barrels a day of imports, now internal production achieves almost 60%% of required oil and around 7million barrels are imported per day. Possibly the OPEC countries are also trying to send the US producers broke by letting production run at a high surplus, pushing the price down. Maybe some of the mid-east countries have high production costs but have heard Saudi costs being sub $30 a barrel, I would say most others around that area would be similar.
As falling leaf has already posted a lot of the US production may be short lived and result in a spike in a few years time as things catch up again.
The price at the pump can sometimes have little to do with the barrel of crude it came from though. It is more related to the cost of getting to that point, where the original refining was done, index price, exchange rates and most importantly what the consumer is prepared to pay for it en masse.