Until we have them in hand no cost comparison can be done. I am postulating based on specs and availability of hardware that Sony will have a cost advantage, assuming they use 8x 4Gb GDDR5 chips rather than 16x 2Gb ones. MS will be using 16x 4Gbit DDR3 chips initially which will increase motherboard complexity and cooling requirements.
At the very least, it means MS will not have a cost advantage as is currently assumed given the lesser power. Having 4Gb chips from the off halves the cost of the most expensive component in Orbis and MS are giving away their GPU savings for ESRAM on the APU.
Cape Verde is 123mm^2, with the extra CUs that pushes it to ~ 150mm^2, the ESRAM adds a further 40mm^2 and adds complexity which will depress yields.
Pitcarin is 212mm^2 but Sony haven't got all 20CUs, whether that is down to yields or they have removed them altogether is not known. The difference is not significant (and if Sony have removed the extra 2 CUs then it's non existent), and given the lesser complexity of Sony's APU, it will have higher yields.
So there you have it. Numbers.