Reuters: Oil major BP Plc said the oil spill in the Gulf of Mexico had cost it $350 million so far, suggesting the final bill could be much higher than many analysts predicted and sending its shares to a six-month low. BP said on Monday the sum referred to the cost of spill response, containment efforts, relief well drilling, payments to the Gulf Coast States to speed up their response plans, some compensation claims and federal costs. The London-based group — which until the leak was …