TechInsights, an analyst firm, have pushed out an estimate on the material costs of Apple's recently-announced iPhone 5. The 16GB model has a total estimated cost price of just $167.50 - just $35 more than the iPhone 4S' cost price.
The most expensive part of the iPhone 5 is the A6 processor, coming in at $28, compared to the cost of the A5 chip in the iPhone 4S. It's also worth noting that the iPhone 5 sports a 1400 mAh battery compared to its predecessor, the iPhone 4S, which features a 1420 mAh battery. This will mean that the A6 processor, and/or its iOS 6 is going to need to be very efficient to give the iPhone 5 more battery life than its predecessor.
Remember, as always, these costs are just pure hardware costs. It doesn't include research and development, various investments in hardware and software, assembly, packaging, shipping, or any other related costs.